Rotatable gantry radiation treatment system

ABSTRACT

A radiation treatment apparatus is described. The radiation treatment apparatus may include a gantry frame and a rotatable gantry structure rotatably coupled to the gantry frame, the rotatable gantry structure being rotatable around a rotation axis passing through an isocenter, with the rotatable gantry structure including a first beam member extending between first and second ends of the rotatable gantry structure. The radiation treatment apparatus may also include a radiation treatment head movably mounted to the first beam member in a manner that allows (i) translation of the radiation treatment head along the first beam member between the first and second ends, and (ii) gimballing of the radiation treatment head relative to the first beam member, the gimballing being characterized by pivotable movement in at least two independent pivot directions defined with respect to the first beam member. Non-coplanar radiation treatment of a tissue volume positioned near or around the isocenter may be achievable with the radiation treatment apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/539,476, filed Nov. 12, 2014, which is a continuation of U.S.application Ser. No. 13/033,571, filed Feb. 23, 2011, now U.S. Pat. No.8,917,813, issued Dec. 23, 2014, which claims the benefit of U.S.Provisional Ser. No. 61/307,847 filed Feb. 24, 2010, and U.S.Provisional Ser. No. 61/371,732 filed Aug. 8, 2010, each of which isincorporated by reference herein. The subject matter of this patentspecification is also related to the subject matter of the followingcommonly assigned applications, each of which is incorporated byreference herein: International Application Ser. No. PCT/US11/25936filed Feb. 23, 2011; U.S. Provisional Ser. No. 61/352,637 filed Jun. 8,2010; U.S. Provisional Ser. No. 61/371,733 filed Aug. 8, 2010; U.S.Provisional Ser. No. 61/371,737 filed Aug. 8, 2010; and U.S. ProvisionalSer. No. 61/371,737 filed Jan. 20, 2011. The subject matter of thispatent specification is also related to the subject matter of thefollowing commonly assigned applications: U.S. Ser. No. 13/088,289 filedApr. 15, 2011 and U.S. Ser. No. 13/033,584 filed Feb. 23, 2011.

FIELD

This patent specification relates to the use of radiation for medicaltreatment purposes. More particularly, this provisional patentspecification relates to radiation treatment systems.

BACKGROUND

Pathological anatomies such as tumors and lesions can be treated with aninvasive procedure, such as surgery, which can be harmful and full ofrisks for the patient. A non-invasive method to treat a pathologicalanatomy (e.g., tumor, lesion, vascular malformation, nerve disorder,etc.) is external beam radiation therapy, which typically uses atherapeutic radiation source, such as a linear accelerator (LINAC), togenerate radiation beams, such as x-rays. In one type of external beamradiation therapy, a therapeutic radiation source directs a sequence ofx-ray beams at a tumor site from multiple co-planar angles, with thepatient positioned so the tumor is at the center of rotation (isocenter)of the beam. As the angle of the therapeutic radiation source changes,every beam passes through the tumor site, but passes through a differentarea of healthy tissue on its way to and from the tumor. As a result,the cumulative radiation dose at the tumor is high and that to healthytissue is relatively low.

The term “radiosurgery” refers to a procedure in which radiation isapplied to a target region at doses sufficient to necrotize a pathologyin fewer treatment sessions or fractions than with delivery of lowerdoses per fraction in a larger number of fractions. Radiosurgery istypically characterized, as distinguished from radiotherapy, byrelatively high radiation doses per fraction (e.g., 500-2000 centiGray),extended treatment times per fraction (e.g., 30-60 minutes pertreatment), and hypo-fractionation (e.g., one to five fractions ortreatment days). Radiotherapy is typically characterized by a low doseper fraction (e.g., 100-200 centiGray), shorter fraction times (e.g., 10to 30 minutes per treatment) and hyper-fractionation (e.g., 30 to 45fractions). For convenience, the term “radiation treatment” is usedherein to mean radiosurgery and/or radiotherapy unless otherwise noted.

Image-guided radiation therapy (IGRT) systems include gantry-basedsystems and robotic arm-based systems. In gantry-based systems, a gantryrotates the therapeutic radiation source around an axis passing throughthe isocenter. Gantry-based systems include C-arm gantries, in which thetherapeutic radiation source is mounted, in a cantilever-like manner,over and rotates about the axis passing through the isocenter.Gantry-based systems further include ring gantries having generallytoroidal shapes in which the patient's body extends through a bore ofthe ring/toroid, and the therapeutic radiation source is mounted on theperimeter of the ring and rotates about the axis passing through theisocenter. Traditional gantry systems (ring or C-arm) delivertherapeutic radiation in single plane (i.e., co-planar) defined by therotational trajectory of the radiation source. Examples of C-arm systemsare manufactured by Siemens of Germany and Varian Medical Systems ofCalifornia. In robotic arm-based systems, the therapeutic radiationsource is mounted on an articulated robotic arm that extends over andaround the patient, the robotic arm being configured to provide at leastfive degrees of freedom. Robotic arm-based systems provide thecapability to deliver therapeutic radiation from multiple out-of-planedirections, i.e., are capable of non-coplanar delivery. AccurayIncorporated of California manufactures a system with a radiation sourcemounted on a robotic arm for non-coplanar delivery of radiation beams.

Associated with each radiation therapy system is an imaging system toprovide in-treatment images that are used to set up and, in someexamples, guide the radiation delivery procedure and track in-treatmenttarget motion. Portal imaging systems place a detector opposite thetherapeutic source to image the patient for setup and in-treatmentimages, while other approaches utilize distinct, independent imageradiation source(s) and detector(s) for the patient set-up andin-treatment images. Target or target volume tracking during treatmentis accomplished by comparing in-treatment images to pre-treatment imageinformation. Pre-treatment image information may comprise, for example,computed tomography (CT) data, cone-beam CT data, magnetic resonanceimaging (MRI) data, positron emission tomography (PET) data or 3Drotational angiography (3DRA) data, and any information obtained fromthese imaging modalities (for example and without limitation digitallyreconstructed radiographs or DRRs).

In one common scenario, the therapeutic source is a linear accelerator(LINAC) producing therapeutic radiation (which can be termed an “MVsource”) and the imaging system comprises one or more independent x-rayimaging sources producing relatively low intensity lower energy imagingradiation (each of which can be termed a “kV source”). In-treatmentimages can comprise one or more (preferably two) two-dimensional images(typically x-ray) acquired at one or more different points of view(e.g., stereoscopic x-ray images), and are compared with two-dimensionalDRRs derived from the three dimensional pre-treatment image information.A DRR is a synthetic x-ray image generated by casting hypotheticalx-rays through the 3D imaging data, where the direction and orientationof the hypothetical x-rays simulate the geometry of the in-treatmentx-ray imaging system. The resulting DRR then has approximately the samescale and point of view as the in-treatment x-ray imaging system, andcan be compared with the in-treatment x-ray images to determine theposition and orientation of the target, which is then used to guidedelivery of radiation to the target.

There are two general goals in radiation therapy: (i) to deliver ahighly conformal dose distribution to the target volume; and (ii) todeliver treatment beams with high accuracy throughout every treatmentfraction. A third goal is to accomplish the two general goals in aslittle time per fraction as possible. Delivering an increased conformaldose distribution requires, for example, the ability to delivernon-coplanar beams. Delivering treatment beams accurately requires theability to track the location of the target volume intrafraction. Theability to increase delivery speed requires the ability to accurately,precisely, and quickly move the radiation source without hitting otherobjects in the room or the patient, or violating regulatory agency speedlimitations.

One or more issues arise with respect to known radiation therapy systemsthat are at least partially addressed by one or more of the preferredembodiments described further hereinbelow. Generally speaking, theseissues are brought about by a tension in known radiation therapy systemsbetween mechanical stability and system versatility, a tension thatbecomes more pronounced as the desired use of radiation therapy expandsfrom head-only applications to applications throughout the body, such as(without limitation) the lungs, liver, and prostate. Robot arm-basedsystems tend to allow for larger ranges of radiation beam angles fordifferent body parts than ring or C-arm gantry-based systems, especiallywhen it is desired to keep the patient couch motionless during theradiation therapy session. Accordingly, robot arm-based systemsgenerally tend to allow for more versatility in the kinds of therapyplans that may be available to the patient in comparison to C-arm andring gantry-based systems. Further in view of the very heavy nature ofmost therapeutic radiations sources, which can weigh hundreds ofkilograms, systems based on mounting of the therapeutic radiation sourceon a C-arm gantry suffer from undesired in-treatment deformation of themount structures, which deformation is difficult to model or predict andleads to beam delivery errors and/or increased therapy planning marginsdue to the inability to precisely and accurately identify where the beamis pointed in three-dimensional space.

Ring gantry-based systems, on the other hand, tend to exhibit relativelyhigh mechanical stability, i.e., less of the deformation problemsexhibited by C-arm gantry-based systems, and thus can reproducibly andaccurately position the radiation source, including doing so atrelatively high mechanical drive speeds. However, as discussed above,gantry-based systems (like C-arm systems) tend to provide a lesser rangeof achievable angles for the introduction of therapeutic radiation intodifferent body parts and, therefore, provide a narrower array ofradiation treatment options as compared to robot arm-based systems.

X-ray tomosynthesis refers to the process of acquiring a number oftwo-dimensional x-ray projection images of a target volume using x-raysthat are incident upon the target volume at a respective number ofdifferent angles, followed by the mathematical processing of thetwo-dimensional x-ray projection images to yield a set of one or moretomosynthesis reconstructed images representative of one or morerespective slices of the target volume, wherein the number of x-rayprojection images is less than that in a set that would be required forCT image reconstruction, and/or the number or range of incidentradiation angles is less than would be used in a CT imaging procedure.Commonly, a plurality of tomosynthesis reconstructed images aregenerated, each being representative of a different slice of the targetvolume, and therefore a set of tomosynthesis reconstructed images issometimes referred to as a tomosynthesis volume. As used herein, theterm tomosynthesis projection image refers to one of the two-dimensionalx-ray projection images acquired during the tomosynthesis imagingprocess.

For purposes of the above terminology, for some preferred embodiments, aset of images that is required for CT image reconstruction is consideredto include images (e.g., 300 or more) generated over a range of incidentangles that is 180 degrees plus the fan beam angle. For some preferredembodiments, the x-ray projection images for constructing atomosynthesis image are taken over an angular range between 1 degree andan angular range value that is less than that needed for a completeprojection set for CT imaging (e.g., 180 degrees plus the fan angle),wherein the number of projection images generated in this range is avalue that is between 2 and 1000. In other preferred embodiments, thex-ray projection images for constructing a tomosynthesis image are takenover an angular range of between 5 degrees and 45 degrees, wherein thenumber of projection images generated in this range is between 5 and100.

X-ray tomosynthesis has been proposed as an in-treatment kV imagingmodality for use in conjunction with radiation treatment systems. InU.S. Pat. No. 7,532,705B2 it is proposed to process thethree-dimensional pre-treatment image information (e.g., a planning CTimage volume) to generate digital tomosynthesis (DTS) reference imagedata of a target located within or on a patient, such as by simulatingx-ray cone-beam projections through the planning CT image volume.Subsequently, with the patient on the treatment bed, DTS verificationimages are generated by acquiring a number of x-ray cone beam images atdifferent angles. Target localization is then performed by comparinglandmarks, such as bony structures, soft-tissue anatomy, implantedtargets, and skin contours in the DTS reference image data and DTSverification image data. In U.S. Pat. No. 7,711,087B2 it is proposed toacquire tomosynthesis image data during a treatment session. Forpurposes of movement tracking during the treatment session,tomosynthesis reconstructed slices are processed directly in conjunctionwith reference CT data in a process that searches for a tomosynthesisreconstructed image that best matches a selected reference CT slice. Theidentity of the particular tomosynthesis reconstructed image that yieldsa maximum degree of match, together with the amount of spatial offsetrequired for that tomosynthesis reconstructed image to achieve the peakmatch, is used to localize the target in three-dimensional space. Thecommonly assigned U.S. Pat. No. 6,778,850, which is incorporated byreference herein, also discloses the use of x-ray tomosynthesis images(more particularly, the use of relatively low clarity intra-treatment 3Dimages of the target region synthesized from a plurality of 2Ddiagnostic images acquired at different angles) of as an in-treatment kVimaging modality.

Cone beam CT (CBCT) has also been proposed as an in-treatment imagingmodality for use in conjunction with radiation treatment systems, insome cases as a kV imaging modality and in other cases as an MV (portal)imaging modality. Whereas conventional CT imaging reconstructs 2D slicesfrom 1D projections through a target volume, the 2D slices then beingstacked to form a 3D volumetric image, CBCT imaging directly constructsa 3D volumetric image from 2D projections of the target volume. As knownin the art, CBCT offers the ability to form a 3D image volume from asingle gantry rotation (more specifically, a rotation of at least 180degrees plus a fan beam angle) about the target volume, whereasconventional CT requires one rotation per slice (for single-rowdetectors) or 1/M rotations per slice (for newer quasi-linear multi-rowdetectors having M rows). CBCT also provides for a more isotropicspatial resolution, whereas conventional CT limits the spatialresolution in the longitudinal direction to the slice thickness.However, because conventional CT systems usually offer a substantiallyhigher degree of collimation near their linear or quasi-linear rowdetectors than can usually be afforded by CBCT systems near theirtwo-dimensional detectors, scattering noise and artifacts are more of aproblem for CBCT systems than for conventional CT systems.

In U.S. Pat. No. 7,471,765B2 it is proposed to use a CBCT imaging systemincluding a kV x-ray tube and a flat-panel imaging detector mounted on aLINAC gantry such that the kV radiation is approximately orthogonal tothe MV treatment radiation from the LINAC. Prior to treatment, a CBCTplanning image is acquired for treatment planning. Subsequently, beforeeach treatment fraction, a CBCT image is acquired and compared to theCBCT pre-treatment planning image, and the results of the comparison areused to modify the treatment plan for that treatment fraction tocompensate for interfraction setup errors and/or interfraction organmotion. Due to limitations in permissible gantry rotation speeds (e.g.,one rotation per minute) which cause the CBCT acquisition time to beslow compared to breathing (or other physiological cycles) of thepatient, a gating scheme synchronized to patient breathing (or otherphysiological cycles) is used during CBCT acquisition to reduce thedeleterious effects of organ motion in the reconstructed images. Alsodue to the relatively slow CBCT acquisition time, the CBCT volume datais generally useful only for patient set-up before each treatmentfraction, and not for intra-fraction motion correction.

X-ray source arrays such as field emission “cold cathode” x-ray sourcearrays represent a promising advance in medical imaging and offerpotential advantages over conventional x-ray tube sources in severalrespects. A conventional x-ray tube usually comprises a tungsten,tantalum or rhenium cathode that is heated to approximately 2000° C. tocause electrons to be emitted thermionically, the free electrons thenbeing accelerated toward an anode by a high electrical potential such as120 kV. X-ray radiation usable for imaging is created when thethermionically generated electrons strike an anode, usually made oftungsten, molybdenum, or copper, at a focal spot of the x-ray tube, thecollision causing the emission of x-ray photons. While historicallybeing the only practical and cost-effective way to provide imaging x-rayradiation in medical imaging environments, conventional x-ray tubesources can bring about many design compromises in view of theirrelatively large size and weight, high operating temperatures, highpower consumption, relatively modest temporal resolution (e.g., on/offswitching times), and their minimal amenability to miniaturization orformation into closely spaced arrays.

As an alternative to conventional x-ray tube technology in which freeelectrons are generated by thermionic emission, alternative technologieshave been introduced in which the free electrons are generated by fieldemission. In a field emission source, free electrons are emitted uponthe application of a voltage to a material having a high emissiondensity, such as certain carbon nanotube (CNT) materials. Because fieldemission of electrons is produced by a high electric field, no heatingis necessary. Field emission sources are thus often referred to as coldcathode sources. Advantageously, the electron beams emitted by suchmaterials may have low divergence and thus provide ease of focusing ontoa focal spot. Moreover, the virtually instantaneous response of thesource offers time gating capabilities that may even be on the order ofnanoseconds. Because they can be made exceedingly small, field emissionx-ray sources are highly amenable To formation into arrays. According toU.S. Ser. No. 07/505,562B2, which is incorporated by reference herein,devices having 1000 pixels per meter (i.e., 1000 individual x-raysources per meter) with pulse repetition rates on the order of 10 MHzcan be envisioned using technology within the current state of the art.

As used herein, the term x-ray source array refers to a source of x-rayscomprising a plurality of spatially distinct, electronically activatiblex-ray emitters or emission spots (focal spots) that are addressable onat least one of an individual and groupwise basis. Although most x-raysource arrays suitable for use with one or more of the preferredembodiments will commonly be of the field emission “cold cathode” type,the scope of the present teachings is not so limited. By way of example,other types of x-ray source arrays that may be suitable for use with oneor more of the preferred embodiments include scanning-beam array X-raysources in which an electron beam digitally scans across a tungstentransmission target thirty times per second, sequentially producing tenthousand individually collimated X-ray beams, as reported by Triple RingTechnologies, Inc., of Newark, Calif.

X-ray source arrays have been proposed for use in kV imaging systemsassociated with radiation treatment systems, such as in US20090296886A1.However, it is believed that substantial advances in the configuration,operation, and/or manner of integration of x-ray source arrays into IGRTsystems, such as those provided by one or more of the preferredembodiments herein, are needed in order to achieve clinicalpracticality, effectiveness, and market acceptance. It is to beappreciated the although particularly advantageous in the context ofIGRT systems, one or more of the preferred embodiments is alsoapplicable to a wide variety of other medical imaging applicationsoutside the realm of image-guided radiation treatment.

More generally, one or more issues arises with respect to known medicalimaging and/or radiation treatment systems that is at least partiallyaddressed by one or more of the preferred embodiments described furtherhereinbelow. Other issues arise as would be apparent to a person skilledin the art in view of the present teachings.

SUMMARY

Provided according to one preferred embodiment is a radiation treatmentapparatus comprising a gantry frame and a rotatable gantry structurerotatably coupled to the gantry frame, the rotatable gantry structurebeing rotatable around a rotation axis passing through an isocenter. Therotatable gantry structure includes a first beam member extendingbetween the first and second ends of the rotatable gantry structure, anda radiation treatment head movably mounted to the first beam member in amanner that allows translation of the radiation treatment head along thefirst beam member between the first and second ends and gimballing ofthe radiation treatment head relative to the first beam member.

Provided according to one or more preferred embodiments are systems,methods, and related computer program products for image-guidedradiation treatment (IGRT), including an image-guided radiation therapy(IGRT) system that provides both high mechanical stability and radiationdelivery and target tracking versatility. The IGRT system is robustagainst deformation even in cases of relatively swift movement of itstherapeutic radiation source, while at the same time providing for awide range of achievable angles for the introduction of therapeuticradiation into different body parts and providing for a wide range ofimaging options for locating and tracking a target region. Therefore,IGRT systems according to one or more of the preferred embodimentsprovide for a wider array of radiation treatment options in relativelyfaster treatment times. In one or more preferred embodiments, the IGRTsystem further includes a highly versatile yet stable in-therapy imagingsystem for further enhancing overall system adaptability, precision, andperformance. In other preferred embodiments, related methods forradiation treatment delivery are provided, including a method forconical non-coplanar rotational arc therapy and cono-helicalnon-coplanar rotational arc therapy.

Further provided according to one or more preferred embodiments aremethods for intra-fraction target tracking in a gantry-style IGRTsystem, the methods being based on comparisons between a pre-acquiredplanning image and intrafraction x-ray tomosynthesis images and/orintrafraction cone beam CT (CBCT) images. The intrafractiontomosynthesis images and/or CBCT images, which can be acquired usingsingle x-ray point sources or x-ray source arrays, such x-ray sourcesoptionally being provided in stereoscopic and/or dual-energy ormulti-energy configurations, can be compared with the pre-acquiredplanning image in accordance with one or more preferred embodiments thatprovide for one or more of streamlined intrafraction computation,reduced patient x-ray dose, and reduced treatment delivery margins, asis described further hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a radiation treatment environment according to apreferred embodiment;

FIGS. 2A-2B illustrate axial and side cut-away views, respectively, ofan image-guided radiation treatment (IGRT) system according to apreferred embodiment;

FIG. 2C illustrates a perspective view of the IGRT system of FIGS. 2A-2Band a schematic diagram of a computer system integral therewith and/orcoupled thereto according to a preferred embodiment;

FIG. 2D illustrates a side cut-away view of an IGRT system according toa preferred embodiment;

FIG. 3A illustrates a side cut-away view of an IGRT system according toa preferred embodiment;

FIG. 3B illustrates a perspective view of a rotatable gantry structureof the IGRT system of FIG. 3A;

FIGS. 4A-4D illustrate radiation treatment head pivoting capability inan IGRT system according to a preferred embodiment;

FIGS. 5A-5B illustrate axial and side cut-away views, respectively, ofan IGRT system according to a preferred embodiment;

FIGS. 6A-6B illustrate axial and side cut-away views, respectively, ofan IGRT system according to a preferred embodiment;

FIG. 6C illustrates a perspective view of a rotatable gantry structureof the IGRT system of FIGS. 6A-6B;

FIG. 7 illustrates the IGRT system of FIGS. 6A-6C as provided with anoptional additional functionality in which kV sources and kV detectorsare axially translatable along their respective beam members.

FIGS. 8A-8B illustrate axial and side cut-away views, respectively, ofan IGRT system according to a preferred embodiment;

FIG. 8C illustrates a perspective view of plural rotatable gantrystructures of the IGRT system of FIGS. 8A-8B;

FIGS. 9A-9C illustrate conical non-coplanar rotational arc therapy andcono-helical rotational arc therapy using an IGRT system according to apreferred embodiment;

FIG. 10 illustrates non-isocentric radiation beam delivery using an IGRTsystem according to a preferred embodiment;

FIG. 11 illustrates non-isocentric radiation beam delivery including acouch kick using an IGRT system according to a preferred embodiment;

FIG. 12 illustrates image guided radiation treatment according to apreferred embodiment;

FIGS. 13A-13B each illustrate front, top, and axial views of an IGRTsystem including one or more x-ray source arrays according to apreferred embodiment;

FIGS. 14-15 each illustrate front, top, and axial views of an IGRTsystem having one or more x-ray source arrays according to a preferredembodiment;

FIG. 16 illustrate an axial view of an IGRT system having one or morex-ray source arrays according to a preferred embodiment;

FIG. 17 illustrates a conceptual diagram of an example of sliding-windowtomosynthesis imaging or sliding-window CBCT imaging according to one ormore preferred embodiments; and

FIGS. 18-20 each illustrate image guided radiation treatment accordingto one or more preferred embodiments.

DETAILED DESCRIPTION

FIG. 1 illustrates a radiation treatment environment 100 within whichone or more of the preferred embodiments is advantageously applied. Theradiation treatment environment 100 includes a reference imaging system102 and an IGRT system 104. Reference imaging system 102 usuallycomprises a high precision volumetric imaging system such as a computedtomography (CT) system or a nuclear magnetic resonance imaging (MRI)system. In view of cost and workflow considerations in many clinicalenvironments, the reference imaging system 102 is often a generalpurpose tool used for a variety of different purposes in the clinic orhospital environment, and is not specifically dedicated to the IGRTsystem 104. Rather, the reference imaging system 102 is often located inits own separate room or vault and is purchased, installed, and/ormaintained on a separate and more generalized basis than the IGRT system104. Accordingly, for the example of FIG. 1, the reference imagingsystem 102 is illustrated as being distinct from the IGRT system 104.Notably, for other radiation treatment environments that are not outsidethe scope of the present teachings, the reference imaging system 102 canbe considered as an integral component of the IGRT system 104.

IGRT system 104 comprises a radiation treatment (MV) source 108 thatselectively applies high-energy x-ray treatment radiation to a targetvolume of a patient P positioned on a treatment couch TC. The MV source108 applies the treatment radiation under the control of a systemcontroller 114, and more particularly a treatment radiation controlsubsystem 128 thereof. System controller 114 further comprisesprocessing circuitry 120, a detector controller 122, a couch positioncontroller 124, and a kV radiation controller 126 each programmed andconfigured to achieve one or more of the functionalities describedfurther herein. One or more imaging (kV) radiation sources 110selectively emit relatively low-energy x-ray imaging radiation under thecontrol of kV radiation controller 126, the imaging radiation beingcaptured by one or more imaging detectors 112. In alternative preferredembodiments, one or more of the imaging detectors 112 can be a so-calledportal imaging detector that captures high-energy x-ray treatmentradiation from MV source 108 that has propagated through the targetvolume.

For one preferred embodiment, the kV imaging radiation sources 110include both a two-dimensional stereotactic x-ray imaging system and atomosynthesis imaging system. For other preferred embodiments, only atwo-dimensional stereotactic x-ray imaging system is provided, while forstill other preferred embodiments only a tomosynthesis imaging system isprovided. Preferably, each of the stereotactic x-ray imaging system andthe tomosynthesis imaging system are characterized by either (a) afixed, predetermined, nonmoving geometry relative to the (x, y, z)coordinate system of the treatment room, or (b) a precisely measurableand/or precisely determinable geometry relative to the (x, y, z)coordinate system of the treatment room in the event they aredynamically moveable. The MV radiation source 108 should also, ofcourse, have a precisely measurable and/or precisely determinablegeometry relative to the (x, y, z) coordinate system of the treatmentroom.

A couch positioner 130 is actuated by the couch position controller 124to position the couch TC. A non-x-ray based position sensing system 134senses position and/or movement of external marker(s) strategicallyaffixed to the patient, and/or senses position and/or movement of thepatient skin surface itself, using one or more methods that do notinvolve ionizing radiation, such as optically based or ultrasonicallybased methods. In one example, IGRT system 104 can be similar to aCYBERKNIFE® robotic radiosurgery system available from AccurayIncorporated of Sunnyvale, Calif., and the position sensing system 134can be similar to relevant sensing components of the AccurayIncorporated SYNCHRONY® respiratory tracking system. IGRT system 104further includes an operator workstation 116 and a treatment planningsystem 118.

In common clinical practice, treatment planning is performed on apre-acquired treatment planning image 106 generated by the referenceimaging system 102. The pre-acquired treatment planning image 106 isoften a high resolution three-dimensional CT image acquiredsubstantially in advance (e.g., one to two days in advance) of the oneor more radiation treatment fractions that the patient will undergo. Asindicated in FIG. 1 by the illustration of an (i, j, k) coordinatesystem for the pre-acquired treatment planning image 106, which is incontrast to the (x, y, z) treatment room coordinate system illustratedfor the treatment room of the IGRT system 104, there is generally nopre-existing or intrinsic alignment or registration between thetreatment planning image 106 coordinate system and the treatment roomcoordinate system. During the treatment planning process, a physicianestablishes a coordinate system (e.g., i, j, k in treatment planningimage 106) within the treatment planning image, which may also bereferred to herein as the planning image coordinate system or planningimage reference frame. A radiation treatment plan is developed in theplanning image coordinate system that dictates the various orientations,sizes, durations, etc., of the high-energy treatment radiation beams tobe applied by the MV source 108 during each treatment fraction. Accuratedelivery of therapeutic radiation to a target requires aligning theplanning image coordinate system with the treatment room coordinatesystem, as the entire delivery and tracking system (if present) iscalibrated to the treatment room coordinate system. It will beappreciated that this alignment does not need to be exact and furtherappreciated that couch adjustment or beam delivery adjustment can beused to account for offsets in the alignment between the two coordinatesystems.

Thus, immediately prior to each treatment fraction, under a preciseimage guidance of the kV imaging radiation sources 110, according to oneor more of the embodiments described further hereinbelow, the patient isphysically positioned such that the planning image coordinate system(defined, for example and not by way of limitation, by a physician whilecreating a treatment plan on a CT image or planning image) is positionedinto an initial alignment with the treatment room coordinate system,hereinafter termed an initial treatment alignment or initial treatmentposition. This alignment is commonly referred to as patient set up.Depending on the location of the target volume, the target volume canvary in position and orientation and/or can undergo volumetricdeformations due to patient movement and/or physiological cycles such asrespiration. As used herein, the term in-treatment alignment variationor in-treatment position variation is used to refer to the variations inposition, orientation, and/or volumetric shape by which the currentstate of the target volume differs from the initial treatment alignment.By virtue of a known relationship between the treatment planningcoordinate system and the treatment room coordinate system, the termin-treatment alignment variation can also be used to refer to thevariations in position, orientation, or volumetric shape by which thecurrent state of the target volume differs from that in the treatmentplanning coordinate system. More generally, the term initial treatmentalignment or initial treatment position refers herein to the particularphysical pose or disposition (including position, orientation andvolumetric shape) of the body part of the patient upon patient setup atthe outset of the treatment fraction.

A non x-ray based position sensing system 134 may also be provided. Thisnon x-ray based position sensing system 134 may include, by way ofexample and without limitation, external markers affixed in some mannerto a patient's chest which move in response to respiration (othermechanisms for monitoring respiration may be used), and include a monoor stereoscopic x-ray imaging system, which as described above canprecisely determine target location. System 134 correlates motion of theexternal markers with target motion, as determined from (for example)the mono or stereoscopic x-ray projections. Non x-ray based positionsensing system 134, therefore, permits system controller 114 to monitorexternal marker motion, use the correlation model to precisely predictwhere the target will be located in real time (e.g., ˜60 Hz), and directthe treatment beam to the target. As treatment of the moving targetprogresses additional x-ray images may be obtained and used to verifyand update the correlation model.

According to a preferred embodiment, system controller 114 includingprocessing circuitry 120 is configured and programmed to receiveinformation from the non-x-ray based position sensing system 134 and theimaging detector(s) 112 or just from the imaging detector(s) 112 whentreating a relatively stationary target volume (for example and withoutlimitation a brain, spine or prostate tumor), compute an in-treatmentalignment variation therefrom, and control the treatment radiationsource 108 in a manner that compensates for the in-treatment alignmentvariation on a continual basis. In the case where the target volumemoves due to respiration, the more information-rich x-ray-based datafrom the imaging detectors 112 is updated at a relatively slow ratecompared to the breathing cycle of the patient (for example, once every15 seconds) to maintain reasonably low x-ray imaging dose levels, theless information-rich data from the non-x-ray based position sensingsystem 134 can be updated in substantially real-time (for example, 30times per second). Using methods such as those described in the commonlyassigned U.S. Ser. No. 06/501,981B1, a correlation model between one ormore x-ray-sensed internal target volume (with our without fiducials)and one or more non-x-ray-sensed external markers is used to ascertainthe in-treatment alignment variations on a real-time basis, thecorrelation model being updated (corrected) at each x-ray imaginginterval. Advantageously, judicious x-ray/tomosynthesis imaging sourcecollimation strategies according to one or more of the preferredembodiments described further infra can be advantageously used toimprove determination of in-treatment alignment variations or targettracking by virtue of one or more of higher x-ray/tomosynthesis imagingquality, reduced x-ray radiation dose, and higher x-ray/tomosynthesisimaging data acquisition rates.

It is to be appreciated that the use of a non-x-ray based positionsensing system 134 such as the SYNCHRONY® respiratory tracking systemrepresents an option that, while advantageous in the radiation treatmentof certain tumors within the lung or chest area, is not required forradiation treatments in many other body parts, such as the prostate,spine or brain. Whereas x-ray dosage concerns provide limits on thenumber of kV x-ray images that should be acquired in any particularintrafraction time interval (for example, no more than one kV imageevery 15 seconds, every 30 seconds, or every 60 seconds), tumors withinthe chest area, liver or pancreas can move at substantially fasterperiodic rates due to respiration, therefore giving rise to the need forthe non-x-ray based position sensing system 134. However, tumors inother parts of the body, such as the prostate, spine or brain, willgenerally experience motion on a much slower time scale, wherein thedose-limited kV x-ray imaging rate will be still be sufficiently high toeffectively guide the radiation treatment. The prostate, for example,may experience movement due to an accumulation of urine in the nearbyurinary bladder, an event for which one kV x-ray image every 60 secondsshould be sufficient to track resultant movement. Accordingly, for themany other parts of the anatomy for which kV imaging rates aresufficient, the non-x-ray based position sensing system 134 and theassociated “real time” tracking (i.e., tracking at a rate faster thanthe kV imaging rate) is not required.

It is to be appreciated that the exemplary radiation treatmentenvironment of FIG. 1 is presented by way of example and not by way oflimitation, that the preferred embodiments are applicable in a varietyof other radiation treatment environment configurations, and that one ormore of the preferred embodiments is applicable to general medicalimaging environments outside the particular context of radiationtreatment systems. Thus, for example, while one or more of the preferredembodiments is particularly advantageous when applied in the context ofa radiation treatment environment in which the reference imaging system102 is physically separated from, has no common coordinate system with,and/or has no other intrinsic means of volumetric image registrationwith the IGRT delivery system 104, the scope of the present teachings isnot so limited. Rather, the one or more preferred embodiments can alsobe advantageously applied in the context of radiation treatmentenvironments in which the reference imaging system is physicallyintegral with radiation treatment delivery system or has other intrinsiclinkages, such as a rail-based patient movement system, with theradiation treatment delivery system.

As used herein, “registration” of medical images refers to thedetermination of a mathematical relationship between correspondinganatomical or other (e.g. fiducial) features appearing in those medicalimages. Registration can include, but is not limited to, thedetermination of one or more spatial transformations that, when appliedto one or both of the medical images, would cause an overlay of thecorresponding anatomical features. The spatial transformations caninclude rigid-body transformations and/or deformable transformations andcan, if the medical images are from different coordinate systems orreference frames, account for differences in those coordinate systems orreference frames. For cases in which the medical images are not acquiredusing the same imaging system and are not acquired at the same time, theregistration process can include, but is not limited to, thedetermination of a first transformation that accounts for differencesbetween the imaging modalities, imaging geometries, and/or frames ofreference of the different imaging systems, together with thedetermination of a second transformation that accounts for underlyinganatomical differences in the body part that may have taken place (e.g.,positioning differences, overall movement, relative movement betweendifferent structures within the body part, overall deformations,localized deformations within the body part, and so forth) betweenacquisition times.

FIGS. 2A-2C illustrate an IGRT system 200 that is capable of carryingout the functionalities described above with respect to the IGRT system104 of FIG. 1 according to one or more preferred embodiments. Includedin FIG. 2C is a diagram of a computer system 250 integrated with theIGRT system 200, the computer system 250 being omitted from FIGS. 2A-2Bfor clarity of description. IGRT system 200 comprises a gantry frame 202within which is disposed a rotatable gantry structure 204 configured torotate around a rotation axis 214 that passes through an isocenter 216.Associated with the IGRT system 200 is an imaginary plane, termed hereina transverse isocentric plane 217, that is orthogonal to the rotationaxis 214 and passes through the isocenter 216. The gantry frame 202, theisocenter 216, the rotation axis 214, and the transverse isocentricplane 217 are preferably fixed and motionless relative to a treatmentvault (not shown) in which the IGRT system 200 is installed. As usedherein, isocenter or machine isocenter is a physical point in atreatment room (treatment vault). A treatment center is a point withinthe target volume defined by a physician during treatment planning,normally based within the pretreatment CT image reference frame. Forisocentric treatment the treatment center is aligned with the machineisocenter during the set up procedure described above.

The rotatable gantry structure 204 includes one or more beam members 206that each extend between first and second ring members 208 and 209disposed on opposite sides of the transverse isocentric plane 217. Thefirst ring member 208 corresponds generally to a first end of therotatable gantry structure 204 (toward the left side of FIG. 2B), whilethe second ring member 209 corresponds generally to a second, oppositeend of the rotatable gantry structure 204 (toward the right side of FIG.2B). The first and second ring members 208 and 209 are supported attheir respective ends of the rotatable gantry structure 204 bycorresponding ends of the gantry frame 202 in a manner that allows andfacilitates rotation of the rotatable gantry structure 204 around therotation axis 214 while keeping the rotation axis 214 highly stable andstationary. The skilled artisan will appreciate that any of a variety ofdifferent mechanical support schemes that allow such rotation can beused (e.g., anti-friction sleeves, slip bearings, roller bearings,etc.). The skilled artisan will appreciate that the gantry frame 202 canbe made substantially thicker or otherwise reinforced at its respectiveends than is indicated schematically in FIG. 2B, in accordance with theparticular materials being used and other design considerations, forensuring such mechanical stability. Without loss of generality, therotatable gantry structure 204 contains two beam members 206 separatedby 180 degrees around the rotation axis 214, which is useful (forexample and without limitation) for facilitating rotational balancing(e.g. by applying appropriate balancing weights to the opposing beammembers 206). The skilled artisan will appreciate that the term beammember as used herein can encompass a wide variety of different types ofstructural members (e.g., solid rods, hollow rods, assemblies ofparallel or concentric rods, truss-type structures, etc.) that canstructurally extend from one place to another and along which one ormore physical items (e.g., LINACs, LINAC assemblies, imaging sources,imaging detectors, and so forth) can be fixably or movably mounted orpositioned.

Movably mounted on one of the beam members 206 is a therapeuticradiation head 210, such as and without limitation a linear accelerator(LINAC) or a compact proton source, which includes thereon an endcollimator 212, such as a multi-leaf collimator (MLC), and whichprovides a therapeutic radiation beam 203. The therapeutic radiationhead 210 can alternatively be termed a radiation treatment head and isdesignated as such in one or more sections hereinbelow. The therapeuticradiation head 210 is mounted to the beam member 206 by a couplingdevice 207 that is configured and adapted to achieve the translationaland rotational functionalities described further hereinbelow. Therotatable gantry structure 204 and therapeutic radiation head 210 aredimensioned so as to allow a central bore 218 to exist, that is, anopening sufficient to allow a patient P to be positioned therethroughwithout the possibility of being incidentally contacted by thetherapeutic radiation head 210 or other mechanical components as thegantry rotates radiation head 210 about patient P. A patient couch 222is provided for supporting the patient P, the patient couch 222preferably being coupled to an automated patient positioning system (notshown) for moving the patient P into a therapy position and manipulatingthe patient with three or more degrees of freedom (e.g., threeorthogonal translations, one parallel to the rotation axis 214, twoorthogonal to rotation axis 214, plus optionally one or more rotations).The skilled artisan will appreciate that many couches can be used inaccordance with embodiments of the present invention.

According to one preferred embodiment, a cylindrically shaped boreshield 220 is provided to line the boundary of the central bore 218. Inaddition to preventing unexpected movement of the patient's hands orother body part into collision with moving parts, the bore shield 220can reduce the sense of intimidation that the patient might feel in viewof the large moving parts in the device. The bore shield 220 providesthe ability to maximize the rotation speed of the gantry, while stillmeeting all regulatory safety requirements. The bore shield 220 shouldbe formed of a material that is substantially transparent to thetherapeutic and imaging radiation, and optionally can be visibly opaqueas well. Also according to a preferred embodiment, the gantry frame 202is configured and dimensioned such that a conical tapering 221 isprovided at one or both ends of the central bore 218. At a given end ofthe central bore 218 (e.g., the left end in FIG. 2B), the conicaltapering 221 can extend from the bore opening to the ring member 208.Depending on the particular body part being treated, patient visibilityinto the surrounding room can be enhanced to provide a lessclaustrophobic experience for the patient. In combination, oralternatively, bore shield 220 could be a structural supporting cylinderor hub to which frame 202 is mechanically connected at approximatelyopposite ends of the supporting cylinder or hub. In such an embodimentthe hub will provide additional or alternative structural support inaddition to or in lieu of frame 202. In another embodiment the hub(whether or not made from radiolucent material) and/or the bore shield220 has a longitudinal slit parallel to rotation axis 214 to allowradiation to pass therethrough unimpeded, thereby reducing thepossibility of the so-called skin effect or to maximize skin sparing. Aswill be appreciated, the bore shield 220 could still line the structuralcylinder and need not necessarily possess the slit, thereby fullyclosing off patient view and access to the rotating radiation source.The slit, if viewable by a patient, could be constructed so as tominimize potential access to the rotating radiation source, and thepatient would likely only see the rotating radiation source when it isat or near the top of the ring pointing approximately vertically down.As will be appreciated, the hub will rotate in approximate unison withthe radiation head. Stated in a different way, as an additional option,the bore shield 220 can be coupled such that it rotates with therotatable gantry structure 204. This provides an option of leaving anopen slit within the bore shield 220 through which the therapeuticradiation beam 203 can pass, which could be used to maximize skinsparing. This obscures the patient's view of most of the moving parts(indeed, unless the beam is somewhere above them they will only see theinside of the bore shield) and allows a free beam path that might beimportant to minimize skin dose, particularly if only a few beams areused. Optionally, to maintain moving components behind a fixed surfacecovering as much as possible in view of skin sparing issues, a removablecover can be provided to “plug” the slit, which would be fitted forrotational therapy treatment. For treatments using just a few (1-4)static beams, where build up is most critical but rotation speed betweenbeams is not, then the slit is kept open. For rotational arc therapytreatments where build up is not critical (because skin dose is smearedout over so many beam directions) but rotation speed is critical, thenthe plug is fitted into the slit. This can be achieved manually inpre-treatment which a totally removable plug, or alternatively there isprovided a mechanically sliding system on the bore shield 220 that cancover and uncover the slit under control and/or actuation of thetreatment technician.

According to a preferred embodiment, the therapeutic radiation head 210is mounted to the beam member 206 in a manner that allows andfacilitates (i) translation of the therapeutic radiation head 210 alongthe beam member 206 (i.e., in an end-to-end manner between first ringmember 208 and second ring member 209), (ii) pivoting of the therapeuticradiation head 210 around a first pivot axis M1, termed herein a primarypivot axis, and (iii) pivoting of the therapeutic radiation head 210around a second axis M2, termed herein a secondary pivot axis, locatedat a right angle to M1. Preferably, the axes M1 and M2 each pass throughthe center of mass (CoM) of the therapeutic radiation head 210, and thecenter of mass lies along the axis of the therapeutic radiation beam 203Collectively, the primary pivoting around axis M1 and the secondarypivoting around axis M2 can be considered as a gimbal or gimballingmotion of the therapeutic radiation head 210. For clarity ofdescription, the primary pivoting around axis M1 may be referencedhereinbelow by the term “M1 pivot” or “M1 pivoting,” and the secondarypivoting around axis M2 may be referenced hereinbelow by the term “M2pivot” or “M2 pivoting.” Notably, the terms primary/M1 and secondary/M2are used herein for identification purposes and are not indicative ofany particular imaging-related or treatment-related relative rankings.For the preferred embodiment of FIGS. 2A-2C, the beam member 206 uponwhich the therapeutic radiation head 210 is mounted is concavely shapedrelative to the rotation axis 214 such that the source-axis distance(SAD) remains approximately fixed for the range of translation distancesof the therapeutic radiation head 210 along beam member 206. Preferably,the axes M1 and M2 pass through the center of mass (CoM) of thetherapeutic radiation head, which is also coincident with the radiationsource (e.g., focal spot in a LINAC). This makes treatment planningsimpler and minimizes SAD variation with gimballing during tracking.Thus, there are three possibilities, each being within the scope of thepresent teachings, with regard to that which the axes M1 and M2 passthrough: CoM of the therapeutic radiation head 210 for mechanicaladvantage; the axis of the therapeutic radiation source for advantage intreatment planning and providing minimal SAD variation with gimballingduring tracking advantage; or both. By way of example, achieving bothfor a LINAC could include the use of balancing weights.

The skilled artisan will appreciate that the IGRT system 200 furtherincludes a plurality of actuators of various types (not shown) forachieving the mechanical functionalities described hereinabove andhereinbelow in the instant disclosure. Thus, for example, the IGRTsystem 200 includes respective actuation devices (not shown) to achievethe rotation of the rotatable gantry structure 204 around the rotationaxis 214, the axial translation of the therapeutic radiation head 210along the beam member 206, the M1 pivoting of the therapeutic radiationhead 210, and the M2 pivoting of the therapeutic radiation head 210. TheIGRT system 200 further includes one or more processing and/or controlunits, such as may be implemented on one or more programmable computers,for controlling the various actuators and sending signals to and fromthe various recited radiation sources and detectors as necessary toachieve the functionalities described hereinabove and hereinbelow in theinstant disclosure. In view of the present disclosure, those skilled inthe art would be able to configure such actuation devices, processingand/or control units, programmable computers, etc., and operate thedescribed IGRT systems without undue experimentation.

Included in FIG. 2C is a schematic diagram of a computer system 250integrated with and/or coupled to the IGRT system 200 using one or morebusses, networks, or other communications systems 260, including wiredand/or wireless communications systems, and being capable in conjunctiontherewith of implementing the methods of one or more of the preferredembodiments. Methods of image guided radiation treatment in accordancewith one or more of the preferred embodiments may be implemented inmachine readable code (i.e., software or computer program product) andperformed on computer systems such as, but not limited to, the computersystem 250, wherein a central processing unit (CPU) 251 including amicroprocessor 252, random access memory 253, and nonvolatile memory 254(e.g., electromechanical hard drive, solid state drive) is operated inconjunction with various input/output devices, such as a display monitor255, a mouse 261, a keyboard 263, and other I/O devices 256 capable ofreading and writing data and instructions from machine readable media258 such as tape, compact disk (CD), digital versatile disk (DVD),blu-ray disk (BD), and so forth. In addition, there may be connectionsvia the one or more busses, networks, or other communications systems260 to other computers and devices, such as may exist on a network ofsuch devices, e.g., the Internet 259. Software to control the imageguided radiation treatment steps described herein may be implemented asa program product and stored on a tangible storage device such as themachine readable medium 258, an external nonvolatile memory device 262,or other tangible storage medium. For clarity of presentation, thecomputer system 250 of FIG. 2C is omitted from further drawings and/ordescriptions hereinbelow. Methods for configuring and programming thecomputer system 250 for achieving the functionalities described hereinwould be apparent to a person skilled in the art in view of the presentdisclosure.

Advantageously, by virtue of the possibilities provided by thecombination of axial translation of the therapeutic radiation head 210,M1 pivoting, and M2 pivoting, a rich variety of radiation treatmentdelivery plans are facilitated by the IGRT system 100, as will bediscussed further infra. At the same time, by virtue of a ring-stylemechanical nature of the rotatable gantry structure 204 (which could bemore particularly referenced as a “barrel-style” mechanical nature), agreater degree of mechanical stability may be provided in comparison toapproaches in which therapeutic radiation head support is of acantilever-like nature. Generally speaking, in addition to positivelyaffecting the range of achievable tilt angles (i.e., the angle betweenthe therapeutic radiation beam 203 and the transverse isocentric plane217 when the therapeutic radiation beam is isocentric, see FIG. 4A),increased end-to-end distance between the ring members 108 and 109 willhave an impact on the mechanical stability of the device. The selectionof the end-to-end distance between the ring members 108 and 109 willalso have an impact on the end-to-end length of the central bore 118,which should not get too long, and the overall height of the gantryframe 202, which should not get too high so that the system may fitwithin most existing radiation treatment vaults.

FIG. 2D illustrates an IGRT system 280 according to another preferredembodiment, comprising a gantry frame 282, a rotatable gantry structure284 including beam members 286 and ring members 288 and 289, and atherapeutic radiation head 290 including an end collimator 292. The IGRTsystem 280 is similar to the IGRT system 200 of FIGS. 2A-2C except thatthe beam member 286 upon which the therapeutic radiation head 290 ismounted is convexly shaped relative to the rotation axis 214. Theconvexity of the beam member 286 accommodates a physically larger endcollimator 292, which for certain MLC designs can have a rather largewidth. Advantageously, the larger end collimator 292 is accommodatedwhile also maintaining a required minimum diameter for a central bore298, and while also providing a desirably lesser SAD as the therapeuticradiation head 290 approaches the transverse isocentric plane 217,whereas the SAD is greater near the ends of the beam member 286 in orderto maintain the diameter of central bore 298.

FIGS. 3A-3B illustrate an IGRT system 300 according to a preferredembodiment, comprising a gantry frame 302, a rotatable gantry structure304 including beam members 306 and ring members 308 and 309, and atherapeutic radiation head 310 including an end collimator 312. The IGRTsystem 300 is similar to the IGRT system 200 of FIGS. 2A-2C except thatthe beam member 306 upon which the therapeutic radiation head 310 ismounted is approximately linear and oriented approximately horizontally.A lesser SAD is provided for therapeutic radiation head 310 at locationsnearer the transverse isocentric plane 217 than for locations nearer theends of the beam member 306.

FIGS. 4A-4D are presented to provide definitions for the functionalgeometry of an IGRT system according to the preferred embodiments, andare presented by way of a nonlimiting example with respect to the IGRTsystem 300 of FIGS. 3A-3B. With reference to FIG. 4A, an axialtranslation distance Dx is defined as a translation distance of thetherapeutic radiation head 310 along the beam member 306 relative to anarbitrary reference point therealong, which can be set at the transverseisocentric plane 217 as in FIG. 4A or at another fixed location alongbeam members 306. A tilt angle θ_(T) is defined as the arc between thetherapeutic radiation beam 203 and the transverse isocentric plane 217when the therapeutic radiation beam 203 is at isocenter. For any fixedposition of the therapeutic radiation head 310 along the beam member306, the tilt angle θ_(T) is fixed. A primary pivot angle θ_(M1), alsotermed an M1 pivot angle, is defined as the net amount the therapeuticradiation head 310 has been rotated around its M1 axis relative to anarbitrary starting orientation therearound, which can be set at parallelto the transverse isocentric plane 217 as in FIG. 4A or at some otherfixed starting orientation. For the particular case of a straight beammember 306 that is approximately horizontal, as in FIG. 4A, the primarypivot angle θ_(M1) is equal to the tilt angle θ_(T) when the therapeuticradiation beam 203 is at isocenter. Illustrated in FIG. 4B is a scenarioin which the primary pivot angle θ_(M1) has changed by a small amountΔθ_(M1) relative to the configuration of FIG. 4A, which has caused thetherapeutic radiation beam 203 to become off-isocenter.

With reference to FIG. 4C, a gantry angle θ_(G) is defined as the netamount the rotatable gantry structure 304 has been rotated around therotation axis 214 relative to an arbitrary starting orientationtherearound, which is illustrated by a vertical line 488 in FIG. 4C.With reference to FIG. 4D, a secondary pivot angle θ_(M2), also termedan M2 pivot angle, is defined as the net amount the therapeuticradiation head 310 has been rotated around its M2 axis relative to anarbitrary starting orientation therearound, which can correspond to astarting case (see FIG. 4C) in which the therapeutic radiation beam 203is at isocenter. Illustrated in FIG. 4D is a scenario in which thesecondary pivot angle θ_(m2) has been moved to a value other than zero,which has caused the therapeutic radiation beam 203 to becomeoff-isocenter. In one preferred embodiment, the M1 and M2 pivot anglesare dynamically varied during treatment to compensate for target volumemotions (caused by, e.g., breathing motions or patient movement) whilethe patient couch 222 remains stationary, thereby facilitating increasedtreatment effectiveness against patient movement while also allowing thepatient to be more comfortable and at-ease as compared to configurationsin which the patient couch 222 is moved. In another preferredembodiment, the M1 and M2 pivot angles are varied to deliver radiationbeams non-isocentrically, which can for example allow the treatment oftargets that are larger than the collimator field size without movingthe patient couch 222.

FIGS. 5A-5B illustrate an IGRT system 500 according to a preferredembodiment that is similar to the preferred embodiment of FIGS. 3A-3B,but with the addition of in-treatment stereoscopic x-ray imaging sources(“kV sources”) 552 and detectors (“kV detectors”) 554. The kV sources552 and kV detectors 554 are positioned in fixed, non-moving positionsrelative to the gantry frame 302 at locations designed to keep them outof contact with the therapeutic radiation head 310 during treatment. ThekV sources 552 and kV detectors 554 are coplanar with the transverseisocentric plane 217. Shown in FIGS. 5A-5B are arrows labeled S_(IMG)that are representative of the imaging radiation passing from each kVsource 552 to its associated kV detector 554. For clarity of descriptionherein, each kV source/detector pairing is referenced as a “kV imagingsystem.” Although in the example of FIGS. 5A and 5B the kV imagingsystems are coplanar with the transverse isocentric plane 217, in otherpreferred embodiments one or more of the kV imaging systems can bepositioned out of the transverse isocentric plane 217. In one preferredembodiment, multiple kV imaging systems can be mounted to define one ormore planes that are coincident with the rotation axis 214.

FIGS. 6A-6C illustrate an IGRT system 600 according to a preferredembodiment, comprising a gantry frame 602, a rotatable gantry structure604 including beam members 606 and ring members 608 and 609, and atherapeutic radiation head 610. The IGRT system 600 is similar to theIGRT system 300 of FIGS. 3A-3B except that the rotatable gantrystructure 604 is further provided with additional beam members 660extending between ring members 608 and 609. The additional beam members660 are each provided with one (or more) kV source(s) 652 and/or one (ormore) kV detectors 654, and are configured such that each kV source 652is paired with an associated kV detector 654 opposite the isocenter.Each kV source 652 is coupled to its respective beam member 606 by arespective coupling device 656, and each kV detector 654 is coupled toits respective beam member 606 by a respective coupling device 658, thecoupling devices 656 and 658 being configured and adapted to achieve thefunctionalities (e.g., fixed, translational, and/or rotational)described further herein. For the preferred embodiment of FIGS. 6A-6C,there are four beam members 660 that establish two kV imaging systems.(FIG. 6C omits one of the kV imaging systems and its associated beammembers for clarity of presentation.) In other preferred embodiments,there may only be a single kV imaging system provided, or more than twokV imaging systems provided. The beam members 660 are disposed atsuitable angles relative to each other and to the therapeutic radiationhead 610 to achieve the desired kV imaging functionality, which caninclude stereoscopic imaging or CT imaging (e.g., cone beam CT or CBCTimaging) when combined with rotation of the kV imaging system about thepatient.

FIG. 7 illustrates the IGRT system 600 of FIGS. 6A-6C as provided withan optional additional functionality in which the kV source(s) 652 andkV detector(s) 654 are axially translatable along their respective beammembers. The kV source(s) 652 (and, optionally, the kV detectors 654)are also provided with pivoting or gimballing ability. As illustrated inFIG. 7, the kV imaging systems have the ability to depart from thetransverse isocentric plane 217 in a variety of different ways. For thepreferred embodiment of FIGS. 6A-6C and FIG. 7, the kV imaging systemsrotate around the rotation axis 214 in unison with the therapeuticradiation head 610.

FIGS. 8A-8C illustrate an IGRT system 800 according to a preferredembodiment in which the kV imaging system(s) rotate independently of thetherapeutic radiation head around the rotation axis. IGRT system 800comprises a gantry frame 802, a first rotatable gantry structure 804including beam members 806 and ring members 808 and 809, and atherapeutic radiation head 810. IGRT system 800 further comprises asecond rotatable gantry structure 874 including beam members 860extending between a first ring member 878 and a second ring member 879,the second rotatable gantry structure 874 being configured and adaptedto rotate concentrically with, and independently of, the first rotatablegantry structure 874 around the rotation axis 214. The IGRT system 800comprises kV source(s) 852 each coupled to their respective beam member806 by a respective coupling device 856, and kV detector(s) 854 eachcoupled to their respective beam member 806 by a respective couplingdevice 858, the coupling devices 856 and 858 being configured andadapted to achieve fixed, translational, and/or rotationalfunctionalities between the kV source(s) 852/kV detector(s) 854 andtheir respective beam members 860. (FIG. 8C omits one of the kV imagingsystems and its associated beam members for clarity of presentation.)Advantageously, because the kV imaging system(s) can rotateindependently of the therapeutic radiation head around the rotationaxis, a wide variety of setup and in-treatment imaging options areprovided, for accommodating a rich variety of radiation therapy profilesand strategies. With regard to the orientation angles between respectivekV imaging systems, 60 degrees or more is desirable for stereoscopiclocalization, while a full 90 degrees is optimal. For the preferredembodiment of FIGS. 5A-5B (static kV imaging system) and the preferredembodiment of FIGS. 8A-8C (fully decoupled from the therapeuticradiation head rotation), the choice of distances from the rotation axis214 is somewhat limited, while for the preferred embodiment of FIGS.6A-6C, in which the kV imaging systems rotate rigidly with thetherapeutic radiation head rotation, that choice of distances is moreflexible, for example, there is the ability to use a smaller kV detectorand reduce the distance from the rotation axis 214.

FIGS. 9A-9C illustrate methods for non-coplanar rotational arc therapyusing, by way of nonlimiting example, the IGRT system 800 of FIGS.8A-8C, a simplified version of which is reproduced in FIG. 9A. In onepreferred embodiment referenced herein as conical non-coplanarrotational arc therapy, the therapeutic radiation head 810 is axiallytranslated along the beam member 806 in discrete steps, with a gantryrotation occurring at each step. There can be discrete firings of thetherapeutic radiation beam at respective discrete gantry angles, orthere can be continuous firings of the therapeutic radiation beam as thegantry angle is continuously changed, each of which are within the scopeof the present teachings. FIG. 9B illustrates a cross-section of theresultant delivery profile for conical non-coplanar rotational arctherapy, with each discrete cone shape 1-5 corresponding to a differenttranslational step of the therapeutic radiation head 810. In anotherpreferred embodiment referenced herein as cono-helical non-coplanarrotational arc therapy, the therapeutic radiation head 810 is translatedalong the beam member 806 as the gantry is rotated. There can bediscrete firings of the therapeutic radiation beam at respectivediscrete gantry angles (and correspondingly discrete translationaladvances of the therapeutic radiation head 810), or there can becontinuous firings of the therapeutic radiation beam as the gantry angleis continuously changed (and correspondingly continuous translationaladvances of the therapeutic radiation head 810), each of which arewithin the scope of the present teachings. FIG. 9C illustrates across-section of the resultant delivery profile for cono-helicalnon-coplanar rotational arc therapy, which spans the same conicalthree-dimensional volume as conical non-coplanar rotational arc therapy,but which does so in a continuous or helical manner.

Although certain examples in the discussion above and below are madewith respect to the IGRT system 800 of FIGS. 8A-8C, which isparticularly versatile, other of the preferred IGRT systems describedhereinabove could also achieve various ones of the functionalitiesdiscussed herein as would be apparent to a person skilled in the art.Thus, it is to be appreciated that references in the discussion aboveand below to the IGRT system 800 of FIGS. 8A-8C are set forth by way ofexample and not my way of limitation.

As illustrated by the examples of FIGS. 9A-9C above, a rich variety ofradiation therapy profiles and strategies can be accommodated using theIGRT system 800. Such possibilities include, but are not limited to:single or parallel opposed static beams with rectangular field shapingand 1D (wedge or virtual wedge using MLC) intensity modulation; staticbeams with rectangular field shaping and 1D modulation; coplanarrotational treatments (“arc therapy”) with rectangular field shaping and1D modulation; coplanar or non-coplanar beams with irregular fieldshaping and 1D modulation (“conformal radiation therapy” or CRT);coplanar or non-coplanar beams with irregular field shaping and 2Dmodulation (“intensity modulated radiation therapy” or IMRT); andtomotherapy (helical or sequential) with coplanar rotation using anarrow beam in combination with couch movement and 2D modulation. Suchpossibilities further include rotational arc therapy, also calledintensity modulated arc therapy (IMAT), including one or more coplanarrotations, irregular field shaping, and 2D modulation, with gantryrotation speed, dose rate, MLC positions, and in some cases collimatorangles being varied during rotation, and including multiple rotationsthat increase the achievable degree of intensity modulation in view ofpractical constraints on MLC motion during treatment.

One of the benefits of the IGRT system 800 is achieving rotational arctherapy with multiple non-coplanar rotations in order to maximize thenumber of beam positions, the solid angle covered by these positions,and the degree of intensity or fluence modulation of the therapeuticradiation beam in order to achieve the highest possible treatment planquality. Another of the benefits of the IGRT system 800 is accuratedelivery of treatment plans using image guidance for patient set up andintra-fraction motion tracking and correction. Another of the benefitsof the IGRT system 800 is increased rigidity, which enables higherrotation speeds, higher delivery accuracy (less error in radiation beamposition and orientation), and higher 3D reconstructed image quality(less error in imaging system geometry during rotation).

For one preferred embodiment, the therapeutic radiation head 810comprises a compact lightweight LINAC, such as an X-band or C-band LINACin a compact configuration without a bending magnet. This allows acompact system design in which all moving components are behind a fixedsurface covering (see bore shield 820), thus eliminating the risk ofcollision with the patient and enabling higher rotation speeds (there isa U.S. regulatory standard that does not allow rotation speeds higherthan one rotation per minute if there is a risk of collision with thepatient). In other alternative embodiment, the compact accelerator caninclude a bending magnet.

By way of example and not by way of limitation, the central bore 818could have a diameter of 85 cm. This will accommodate the vast majorityof patients. The therapeutic radiation head 810 could be a LINAC havinga distance from the radiation source target to the distal face of theend collimator 812 of 40 cm. In this case the SAD is approximately 82.5cm (40 cm plus half of 85 cm) when the therapeutic radiation head 810 isin the transverse isocentric plane 217 (zero tilt angle). When the LINACis tilted off axis by 30 degrees, the SAD is approximately 89.1 cmassuming negligible collimator size. The LINAC could have a length ofapproximately 214 cm. The outer diameter of the gantry frame 802 wouldthen be approximately 3.1 m, which will fit within most existingtreatment vaults. When the LINAC is tilted off axis by 30 degrees, theSAD will be larger than 89.1 cm with an actual collimator in order tokeep the collimator outside the gantry bore. The SAD will increase withcollimator size.

For one embodiment, external cables could be run to the therapeuticradiation head 810, the kV imaging systems, and the relevant actuatorsto provide electrical power and signals. This would require gantryrotations in alternating directions in order to wind and unwind thecables. More preferably, the rotatable gantry structure 804 androtatable gantry structure 874 are configured with slip-ring technology,as known to the skilled artisan, for providing power and signals tothese devices.

The therapeutic radiation head 810 could be a LINAC configured withdifferent secondary collimation systems, including fixed cones, avariable aperture collimator such as the Iris Variable ApertureCollimator (Accuray Incorporated, Sunnyvale, Calif.), a binary(tomotherapy) collimator, or an MLC. The LINAC could optionally beconfigured with rectangular jaws.

In the discussion that follows, the therapeutic radiation head 810 isassumed to be a LINAC by way of example only and not by way oflimitation, and the phrases “rotating the gantry” or “gantry rotation”refer to rotation of the rotatable gantry structure 804. Advantageously,there are many possible modes of operation for the IGRT system 800. TheLINAC can rotate about the patient without tilting off axis. In thiscase it could treat at a discrete set of fixed gantry rotation angles(coplanar beams) with or without irregular field shaping and with orwithout modulation, thus enabling coplanar static beams, CRT, and IMRT.For each fixed gantry rotation angle, the LINAC can be tilted off axisat a tilt angle, thus enabling non-coplanar CRT and IMRT. Alternatively,the LINAC could be configured with a binary collimator or an MLC anddeliver radiation while continuously rotating without tilting off axis.By combining the LINAC rotation with patient movement through thecentral bore 818, which can be accomplished for example by lineartranslation of the patient couch 222, sequential or helical tomotherapyis enabled. Alternatively, the LINAC could be configured with a MLC anddeliver radiation while rotating the gantry without tilting off axis.The gantry rotation speed, dose rate, MLC shapes, and collimator anglecould be varied during gantry rotation, thus also enabling conventionalcoplanar rotational arc therapy. By also tilting the LINAC off axis asthe gantry angle is varied, it is possible to deliver rotational arctherapy with multiple non-coplanar rotations in order to maximize thenumber of beam positions, the solid angle covered by these positions,and the degree of intensity or fluence modulation in order to achievethe highest possible treatment plan quality. In one approach, the tiltangle is held constant while the gantry angle is varied. In anotherapproach, the tilt angle is varied while the gantry angle is also varied(see FIGS. 9A-9C, conical non-coplanar rotational arc therapy andcono-helical rotational arc therapy). This approach could be combinedwith movement of the patient couch 222 during gantry rotation to providewhat is termed herein conical non-coplanar tomotherapy or cono-helicalnon-coplanar tomotherapy. Because of the ability to achieve manyorientations using gantry rotation (between 0 and 360 degrees) andmoving the source out of plane by varying the tilt angle (within themaximum limits of the system, which could for example be −30 to +30degrees, or −45 to +45 degrees), breast treatments with parallel opposedfields could be easily and quickly performed by setting the appropriategantry rotation and tilt angles.

With one kV imaging system or less preferably with a portal imagingsystem, the system can acquire X-ray images during gantry rotation. Thesequence of X-ray images can be used to reconstruct a cone beam CT(CBCT) image with many images acquired over at least 180 degrees ofrotation. With fewer images acquired during a rotation of less than 180degrees, the images can be used to reconstruct a tomosynthesis image. ACBCT image with a longer axial field of view can be reconstructed from asequence of X-ray images acquired while moving the patient couch duringgantry rotation. A CBCT image can be used for patient set up for exampleby registration of the CBCT to the planning CT image and aligning thetarget volume with isocenter in accordance with information obtainedfrom the image registrations by adjusting the position of patient couch222. The patient couch 222 could be used to correct for translationoffsets and some or all rotation offsets between the CBCT image and theplanning, pre-treatment CT image. Because of the ability to achieve anyorientation defined by a gantry rotation angle and a tilt angle, allrotation offsets can be handled by adjusting the rotation and tiltangles appropriately. With two (or more) kV imaging systems, the systemcan acquire stereo X-ray images simultaneously or closely in time. Thetwo (or more) X-ray images can be used for patient set up for example byregistration of the X-ray images to digitally reconstructed radiographs(DRRs) generated from the planning CT image. With two kV imagingsystems, it is possible to acquire X-ray images from both systems duringgantry rotation. The images can be acquired simultaneously orinterleaved to reduce scatter. If the imaging systems are mountedperpendicular to each other, it is possible to acquire all X-ray imagesrequired for CBCT image reconstruction with 90 degrees of gantryrotation rather than 180 degrees.

The ability to generate intra-treatment stereoscopic images or CBCTimages allows for intra-fraction target motion tracking. Intra-fractionmotion tracking and correction helps enable better treatment plans andthe accurate delivery of those treatment plans. A system for correlatingtarget motion with motion of an anatomical feature of the body (forexample and without limitation external chest wall or a moving boneystructure) can also be included in embodiments of the present invention.For example, a lung tumor will move periodically with respiration, andthe tumor location can be correlated with (for example and withoutlimitation) motion of the chest wall as the patient breaths (Accuray'sSynchrony® System works in this manner). A camera can be fixed insidethe bore shield 820 to monitor the motion of beacons placed on theexternal chest wall, which motion is correlated to the motion of thetarget due to respiration. Furthermore automated control of the M1 andM2 pivot angles during the fraction can be used to continuously aim theradiation beam at the desired location of a moving target. Other ways ofmoving the radiation beam to track with the moving target using theembodiments of the present invention will be appreciated by the skilledartisan.

With two or more kV imaging systems, the system can acquire stereo X-rayimages simultaneously at any gantry rotation angle. With one kV imagingsystem, the system can acquire stereo X-ray images non-simultaneously atdifferent gantry rotation angles (separated for example by 90 degrees).Advantageously, a compact design is provided in which all movingcomponents are behind a fixed surface covering, thus eliminating therisk of collision with the patient and enabling higher rotation speedsthan with conventional C-arm gantry systems. A higher gantry rotationspeed allows the time between the sequential images to be reduced andfor some applications this may provide sufficiently accurate trackingresults.

Advantageously, also provided by the IGRT system 800 is a capability forsliding CBCT reconstruction. For one preferred embodiment, the rotatablegantry structure 874 can rotate synchronously with the rotatable gantrystructure 804 (or, alternatively, the IGRT system of FIGS. 6A-6C can beemployed). A CBCT can be reconstructed from a set of X-ray imagesacquired by the kV imaging system(s) during gantry rotation. Oneapproach is to acquire X-ray images during gantry rotation, reconstructthe CBCT image, register it to the planning CT image, adjust the patientposition as necessary, then begin treatment delivery. As rotationcontinues, additional X-ray images are acquired, and a continuouslysliding window of the last N images (where N is variable, and can forexample be the number of images corresponding to 180 degrees ofrotation) is used to reconstruct a sequence of CBCT images, oralternatively a sufficient number of images are obtained to construct anew CBCT image. The newer images may replace older images at similargantry angles, thereby updating the CBCT with newer images.Alternatively, when sufficient images become available a new CBCT can begenerated to replace the previous CBCT. These CBCT images can be usedfor tracking and also for dose reconstruction. In other preferredembodiments, the rotatable gantry structure 874 can rotate independentlyof the rotatable gantry structure 804 for providing the CBCT images.Particularly where the decoupled rotatable gantry structure 874 isrotated at a relatively high rotation speed, which can advantageously beachieved in a stable manner by the IGRT system 800, a rich variety ofnew applications facilitated by real-time or quasi-real-time CBCTimaging are made possible including, but not limited to, cardiacapplications.

FIG. 10 illustrates non-isocentric beam delivery according to apreferred embodiment. It is an illustration of treatment with atreatment center T not at isocenter C. It is a method of increasing thetilt angle beyond what is otherwise possible for isocentric treatment.This can be especially useful for cranial applications but is alsopotentially useful for many extracranial applications. If the treatmentcenter is moved along the rotation axis 214, then the therapeuticradiation beam can be made to go through the treatment center for allgantry rotation angles using an appropriate and fixed pivot about the M1axis. Thus, advantageously, radiation treatment can be effectivelyprovided for treatment centers not at isocenter. For a treatment centeron the rotation axis 214, the radiation beam can be made to go throughthe treatment center with a fixed pivot about M1 axis.

FIG. 11 illustrates using a so-called “couch kick” (moving the patientcouch) in another mode of operation particularly useful for cranialtreatments. This, in combination with the concepts above and in FIG. 10for which a treatment center is not at isocenter, increases theavailable orientations for radiation beams going through the head.

According to another preferred embodiment (not shown) and described withrespect to FIGS. 2A-2C above, there is provided a system in which thebeam member 206 can be actuably moved outward and inward relative to theaxis of rotation 214. For such preferred embodiment, the ends of thegantry frame 202 are preferably not tapered as in FIGS. 2A-2C, butrather are straight (planar) for easier mechanical implementation. Thering members 208 are also straight (planar) and made with a larger outerradius to accommodate different beam distances from the rotation axis214. By such actuation the therapeutic radiation head 210 can be movedcloser or further from the rotation axis 214, changing the SAD, even ata fixed translation distance along the beam member 206. Anotheradvantage, in combination with the concepts for FIGS. 10 and 11, is anability to keep the LINAC closer to the head (smaller SAD) forintracranial treatments and yet make the IGRT system versatile enoughfor other body parts.

FIG. 12 illustrates image guided radiation treatment usingsliding-window tomosynthesis imaging according to a preferredembodiment. The method of FIG. 12 is preferably carried out using agantry-style IGRT apparatus having a rotatable gantry structure and atreatment guidance imaging system, the treatment guidance imaging systembeing mounted to and rotatable with the rotatable gantry structure andhaving an x-ray cone beam projection imaging capability. At step 1202, apre-acquired image data set is received, such as the 3D reference image106 discussed supra with respect to FIG. 1, and which can alternativelybe termed a planning image data set or reference image data set. Thepre-acquired image data set, as that term is used herein, can refer notonly to a particular 3D image volume that was acquired, but canalternatively refer to any expression or abstraction of that sameinformation, such as DRRs or DRTs (digitally reconstructed tomographs)generated from that 3D image volume.

FIGS. 13A-16 illustrate selected examples of IGRT systems that can beused in carrying out the method of FIG. 12, as well as the methods ofFIGS. 18-20 that are discussed further infra. It is to be appreciatedthat FIGS. 13A-16 are but a few examples of the many different IGRTsystem configurations that can be used in conjunction with the disclosedmethods, and are disclosed by way of example only and not by way oflimitation.

FIG. 13A illustrates, in an orthographic projection format (i.e.,including front, top, and side views), an IGRT system 1300 that issimilar in certain respects to the IGRT system of FIGS. 6A-6C, supra.The IGRT system 1300 comprises a barrel-style rotatable gantry structureG including beam members g1-g3 that rotate in unison around an axis ofrotation through a range of gantry angles θ_(G). A radiation treatmenthead (therapeutic radiation source) “MV” is mounted to the beam memberg2, an x-ray source array “XSA” is mounted to the beam member g1, and adigital detector array “D” is mounted to the beam member g3. For onepreferred embodiment, the x-ray source array XSA comprises acomputer-steerable electron beam and a spatial arrangement of metallictargets, each metallic target becoming an active x-ray focal spot whenthe electron beam is steered onto it, such as one or more such devicesdeveloped by Triple Ring Technologies, supra. However, other types ofx-ray source arrays, such as cold-cathode source arrays, canalternatively be used. In other preferred embodiments, a conventionalx-ray point source can be used instead of the source array XSA. Moregenerally, for each of the illustrations of FIGS. 13A-16 there is analternative preferred embodiment that is also within the scope of thepresent teachings in which one or more of the source arrays XSA isreplaced by a conventional x-ray point source.

The x-ray source array XSA comprises a number of individual x-raysources that are individually activatible, each individual x-ray sourceemitting x-ray radiation that is collimated, such as by an integralcollimation device or an external collimation device (not shown) placedbetween that source and the target, into an x-ray cone beam that isprojected through the body part and onto the digital detector array D.Any or all of the radiation treatment head MV, x-ray source array XSA,and digital detector array D can be pivotably and/or slidably mounted tothe rotatable gantry structure G and correspondingly actuable undercomputerized control. Although digital detector arrays D are illustratedin the examples of FIGS. 13A-16 as being mounted on gantry beamsopposite the x-ray source arrays, it is to be appreciated that the scopeof the present teachings is not so limited, and that in other preferredembodiments one or more of the digital detector arrays D can bestatically positioned (for example, immediately beneath the patientcouch, or at selected floor or ceiling locations), or attached to therotatable gantry structure in other suitable imaging configurations.

By virtue of a population of x-ray cone beam projection images acquiredby operation of the x-ray source array XSA and digital detector array D,either or both of a tomosynthesis imaging capability and cone beam CT(CBCT) capability can be provided. Where a sufficient population ofx-ray cone beam projection images is acquired over an imaging arc of atleast 180 degrees plus a fan beam angle associated with the x-raysources (termed herein a “minimum CBCT arc”), a three-dimensional CBCTreconstruction algorithm can be used to generate a CBCT volume, which isa “true” three-dimensional representation of the imaged volume. As knownin the art, CBCT imaging can be differentiated from conventional CTimaging in that there is generally no collimation taking place at thedetector, whereas conventional CT imaging involves a high degree ofcollimation at the detector, and therefore a CBCT volume will typicallyhave an appreciably greater amount of noise due to scattering than aconventional CT volume. However, as also known in the art, CBCT imagingis generally faster and more easily implemented than conventional CT andrepresents a more realistic in-treatment imaging modality thanconventional CT.

For cases in which the imaging arc is less than 180 degrees plus the fanbeam angle (the minimum CBCT arc), a tomosynthesis reconstructionalgorithm can be used to generate a tomosynthesis reconstructed volume.As known in the art, a tomosynthesis reconstructed image volume is lessthan “true” in that any particular slice therein will containcontributions from anatomical structures lying throughout the imagedvolume, albeit in blurred form for structures lying outside thatparticular slice location. Although tomosynthesis reconstructed imagevolumes are generally of lesser quality and are more artifact-laden thanCBCT images, tomosynthesis imaging provides an advantage that it issubstantially faster to implement and, particularly for lesser imagingarcs, can be performed in near-real time or even real time, which isespecially useful for in-treatment image guidance. According to onepreferred embodiment, resolution loss associated with limited imagingarc, which is particularly heavy along an axis leading away from thex-ray source, is at least partially remedied by the use of stereoscopictomosynthesis imaging.

FIG. 13B illustrates an IGRT system 1350 that is similar to the IGRTsystem 1300 of FIG. 13A, except with the addition of a stereoscopictomosynthesis imaging capability. In particular, dual x-ray sourcearrays XSA1 and XSA2 and their associated digital detector arrays D1 andD2 are disposed in a stereoscopic imaging configuration relative to thetreatment volume. For the example of FIG. 13B, the x-ray source arraysXSA1 and XSA2 are mounted on the same gantry beam g2, therefore being ata common rotational offset with respect to the axis of rotation of therotatable gantry structure, and are positioned at different longitudinalpositions therealong to define the stereoscopic imaging angle. For onepreferred embodiment the stereoscopic imaging angle (i.e., theseparation in incidence angle between the two “channels” of thestereoscopic configuration) is about 90 degrees, in other preferredembodiments is between 75 and 105 degrees, in still other preferredembodiments is between 45 and 135 degrees, and in still other preferredembodiments is between 25 and 155 degrees. For one preferred embodiment,respective tomosynthesis reconstructed image volumes based on the imagedata from the two stereo “channels” can be combined into a singletomosynthesis reconstructed volume, which is then processed according tothe method of FIG. 12. Alternatively, the respective tomosynthesisreconstructed image volumes can be processed separately according to oneor more of the steps of FIG. 12 and the results subsequently combined.

FIG. 14 illustrates an IGRT system 1400 that is similar to the IGRTsystem 1300 of FIG. 13A, except that a cantilever-style rotatable gantrystructure is used rather than a barrel-style rotatable gantry structure.In other preferred embodiments, a ring-style rotatable gantry structure(not shown) can be used in conjunction with the methods of FIG. 12 andFIGS. 18-20. A variety of other rotating-gantry structures having atleast one x-ray cone beam source mounted thereon are also within thescope of the present teachings.

FIG. 15 illustrates yet another non-limiting example of an IGRT deliveryarchitecture that can be used in conjunction with the described methods.FIG. 15 illustrates an IGRT system 1500 including a barrel-style gantryG having beam members g1-g5, a radiation treatment head MV, and dualsource-detector pairs XSA1-D1 and XSA2-D2 configured in a stereoscopicimaging configuration. However, unlike the stereoscopic configuration ofFIG. 13B, the source-detector pairs are mounted at a common longitudinalposition along the rotatable gantry structure and positioned atdifferent rotational offsets with respect to the axis of rotation todefine the stereoscopic imaging configuration. A variety of differentcombinations of the longitudinal-offset configuration of FIG. 13B andthe rotational-offset configuration of FIG. 15 to define thestereoscopic imaging configuration are also within the scope of thepresent teachings.

FIG. 16 illustrates yet another non-limiting example of an IGRT deliveryarchitecture that can be used in conjunction with the described methods.FIG. 16 illustrates an IGRT system 1600 (side view only) that is similarto the IGRT system 1500 of FIG. 15, except that the stereoscopictomosynthesis imaging hardware is mounted on a first rotatable gantrystructure (having beam members g1-g5) and the radiation treatment headMV is mounted on a second rotatable gantry structure (having beam memberh1). The second rotatable gantry structure rotates concentrically with,and independently of, the first rotatable gantry structure.

By way of example and not by way of limitation, the method of FIG. 12 isdiscussed further hereinbelow with respect to the exemplary IGRT system1300 of FIG. 13A. At step 1204, during a patient setup interval, thepatient is positioned into an initial treatment position relative to theIGRT system under the guidance of the treatment guidance imaging system.Without limitation, the source-detector pair XSA-D of the treatmentguidance imaging system can be used to guide the patient setup process(using, for example, tomosynthesis, CBCT, or stereo x-ray imagingguidance) or, alternatively, a separate component of the treatmentguidance imaging system, such as a separate on-board CBCT, ultrasound,tomosynthesis, or stereo x-ray imaging system, can be used to guide thepatient setup process. At step 1206, after the beginning of radiationtreatment delivery, the x-ray cone beam imaging source (e.g., x-raysource array XSA) and the imaging detector (e.g., the digital detectorarray D) are operated to acquire a first population of x-ray cone beamprojection images of the body part for a respective first population ofgantry angles and acquisition times. At step 1208, the first populationof x-ray cone beam projection images is processed to compute therefrom atime sequence of sliding-window tomosynthesis reconstructed imagevolumes. The time sequence of sliding-window tomosynthesis reconstructedimage volumes is characterized in that each subsequent member of thesequence is computed using at least one same x-ray cone beam projectionimage that was used in computing at least one previous member of thetime sequence.

FIG. 17 illustrates a conceptual plot 1701 of gantry angle θ_(G) versustime “t” during a treatment fraction. Although for clarity of disclosurethe gantry angle trajectory is shown as a straight line in FIG. 17,which is indicative of a scenario in which the rotatable gantrystructure rotates in the same direction at a constant rate, thedescribed methods are applicable for a wide variety of different gantryangle trajectory scenarios in which the rotatable gantry structure canaccelerate, decelerate, stop, reverse direction, and so forth, as wouldbe apparent to a person skilled in the art in view of the presentdisclosure. Shown conceptually in FIG. 17 by points small circles “p”are x-ray cone beam projection images acquired during the treatmentfraction. Each small circle “p” can represent a single x-ray cone beamprojection image as may be acquired by a point source or a single memberof an x-ray source array, or can alternatively represent many differentx-ray cone beam projection images acquired at very closely spaced pointsin time. As illustrated in FIG. 17, respective overlapping subsets ofx-ray cone beam projection images 1702, 1704, and 1706 (a “slidingwindow”) are used to compute respective members tomo(t_(n−1)),tomo(t_(n)), and tomo(t_(n+1)) of a time sequence of tomosynthesisreconstructed images. For one preferred embodiment, at least 50% of thex-ray cone beam projection images used to compute one member of thesequence of tomosynthesis reconstructed images are also used (morespecifically, “re-used”) to compute the next member of the sequence.

With reference again to FIG. 12, at step 1210 treatment radiation isdelivered to the body part based at least in part on a comparisonbetween each of the time sequence of sliding-window tomosynthesisreconstructed image volumes and the pre-acquired image data set. The useof sliding-window tomosynthesis reconstructed image volumes (andsliding-window CBCT volumes, see FIG. 19 infra) has been foundadvantageous in that an at least partially morphable or morphingcharacteristic or quality is imparted thereto that facilitates improvedobject identification and object tracking over time. The use ofsliding-window tomosynthesis reconstructed image volumes (andsliding-window CBCT volumes) has also been found advantageous in that abeneficial balance is provided among the competing requirements ofangular sufficiency of the data set, timewise newness of the data set,and anatomical similarity of adjacent members of the time sequence ofreconstructed volumes. Another advantage is that, upon computation ofone tomosynthesis reconstructed image volume, selected linearmathematical combinations among the re-used x-ray cone beam projectionimages (when there are a plurality of such re-used images) that wereperformed for the one tomosynthesis reconstructed image volume do notrequire recomputation for the next tomosynthesis reconstructed imagevolume in the sequence, thereby making the overall computational processmore efficient.

FIG. 18 illustrates a method for advantageous multipurpose use of apopulation of x-ray cone beam projection images that can be optionallyintegrated into the method of FIG. 12, supra, wherein a commonpopulation of x-ray cone beam projection images is used in creating bothan initial CBCT volume and selected initial tomosynthesis volumes forfacilitating treatment guidance in an image guided radiation treatmentsystem. At step 1802, with the body part in an initial treatmentposition (or alternatively at some other starting point in time duringsetup, upon setup, or near a beginning of the treatment delivery, termedherein an initial time), an initial population of x-ray cone beamprojection images sufficient for creating a CBCT volume (i.e., extendingover the minimum CBCT arc) is acquired. For preferred embodiments inwhich an x-ray source array is used, the CBCT volume will be what istermed herein an x-ray source array CBCT (XSA-CBCT) volume. At step1804, an initial CBCT volume CBCT(0) is computed from the initialpopulation x-ray cone beam projection images, and at step 1806 a firstregistration is computed between CBCT(0) and the pre-acquired imagevolume. At step 1808 (which corresponds generally to steps 1206-1208 ofFIG. 12, supra) intrafraction x-ray cone beam projection images areacquired and processed to form a tomosynthesis volume tomo(t).

As with any tomosynthesis imaging process, there will be a certaintomosynthesis imaging arc (i.e., a set of angles of incident x-rayradiation upon the subject volume) associated with the particular subsetof intrafraction x-ray cone beam projection images that were used tocompute tomo(t) at step 1808. By way of explanation, let thistomosynthesis imaging arc be represented by the range (θ_(MIN)(t),θ_(mAX)(t)). For a scenario in which a single x-ray point source isused, the range (θ_(MIN)(t), θ_(mAX)(t)) will be defined according tothe range of gantry angles traversed when acquiring the subset of x-raycone beam projection images. For a scenario in which an x-ray sourcearray is used and the gantry is not rotating during the particularacquisition interval in question, the range (θ_(MIN)(t), θ_(mAX)(t))will be defined according to the imaging angles subtended by thedifferent x-ray point sources as determined by their respectivepositions on the surface of the source array. For a scenario in which anx-ray source array is used and the gantry is indeed rotating during theparticular acquisition interval in question, the range (θ_(MIN)(t),θ_(MAX)(t)) will be defined according to a combination of the gantryangle traversed and the range of imaging angles subtended across thesurface of the array. According to a preferred embodiment, at step 1810,for any particular intrafraction tomosynthesis volume tomo(t), there isidentified a subset of the initial population of x-ray cone beamprojection images used to construct CBCT(0) that correspond intomosynthesis imaging arc to the tomosynthesis imaging arc for tomo(t),i.e., that correspond to the incidence range (θ_(MIN)(t), θ_(mAX)(t)).

At step 1812, the subset of the initial population of x-ray cone beamprojection images identified at step 1810 is then processed to form aseparate tomosynthesis volume, which is referenced herein as anarc-MATCHED tomosynthesis volume tomo_(MATCHED(t))(0). Advantageously,there will be an intrinsic, inherent registration betweentomo_(MATCHED(t))(0) and CBCT(0) because they are computed using thesame set of x-ray cone beam projection images. Therefore, the firstregistration between CBCT(0) and the pre-acquired image volume (e.g.,planning CT) that was computed at step 1806 can be re-used to serve asthe registration between tomo_(MATCHED(t))(0) and the pre-acquired imagevolume. At step 1814, a second registration between the intrafractiontomosynthesis volume tomo(t) and the arc-MATCHED tomosynthesis volumetomo_(MATCHED(t))(0) is computed. Finally, at step 1816, a registrationbetween tomo(t) and the pre-acquired image volume is computed based on(i) the first registration between CBCT(0) and the pre-acquired imagevolume, (ii) the inherent registration between tomo_(MATCHED(t))(0) andCBCT(0), and (iii) the second registration between tomo(t) andtomo_(MATCHED(t))(0). Treatment radiation is then delivered to the bodypart based at least in part on the results of the registration performedat step 1816.

Advantageously, the method of FIG. 18 provides the speed advantagesassociated with tomosynthesis-based image guidance during theintrafraction time frame, while also providing the precision advantagesassociated with the use of a full CBCT volume when performing theregistration to the pre-acquired image volume (e.g., planning CT image).The latter aspect is particularly advantageous since registrationbetween image volumes acquired using different imaging systems havingdifferent frames of reference—a process that could be called a“bridging” registration—can be a particularly difficult and error-proneprocess, and therefore it is advantageous to base the “bridging”registration on a higher quality CBCT image volume rather than a lowerquality tomosynthesis volume. At the same time, the method of FIG. 18only requires that the “bridging” registration be performed one time,upon acquisition of CBCT(0), and preferably prior to the onset ofradiation delivery when time constraints are not critical. These samehigh-quality registration results can then be re-used during theradiation delivery period, when time constraints are more crucial toeffective intrafraction target tracking. Advantageously, during theradiation delivery period when the time constraints are indeed morecrucial, there are only “non-bridging” registrations required betweentomo(t) and tomo_(MATCHED(t))(0), which can be quickly and reliablyperformed since those volumes were acquired using the same set ofimaging hardware having a common frame of reference.

Image-guided radiation treatment according to the method of FIG. 12,which can optionally include the method of FIG. 18, will usually involverepetition of steps 1206-1210 throughout the treatment fraction,including the computation of a latest (i.e., most recent) member of thetime sequence of sliding-window tomosynthesis reconstructed imagevolumes, comparing that latest member with the pre-acquired image dataset, and delivering treatment radiation to the body part based on theresults of that comparison. As used herein, the term latest gantry anglerefers to the gantry angle associated with the most recent x-ray conebeam projection image used to form the latest member of the sequence ofsliding-window tomosynthesis volumes. For one preferred embodiment,computation of the latest member of the sequence comprises receiving afirst parameter indicative of a desired tomosynthesis reconstructioncoverage arc, identifying from the acquired population of x-ray conebeam projection images a first subset thereof having correspondinggantry angles that are within the desired tomosynthesis reconstructioncoverage arc of the latest gantry angle, and computing the latest memberof the sequence of sliding-window tomosynthesis volumes based on thatfirst subset. The tomosynthesis coverage arc will usually be about 6degrees at a minimum and 180 degrees at a maximum, although the scope ofthe preferred embodiments is not so limited. As used herein, latestacquisition time refers to the time of acquisition of the most recentx-ray cone beam projection image used to form the latest member of thesequence of sliding-window tomosynthesis volumes. For one preferredembodiment, computation of the latest member of the sequence comprisesreceiving a second parameter indicative of a desired data agingthreshold, identifying from the first subset of x-ray cone beamprojection images a second subset thereof having correspondingacquisition times that are within the desired data aging threshold ofthe latest acquisition time, and computing the latest member using onlythat second subset of x-ray cone beam projection images.

The method can further comprise evaluating the percentage of x-ray conebeam projection images that are being re-used between the latest memberof the time sequence of sliding-window tomosynthesis image volumes andthe immediately preceding member of the sequence, this percentage beingtermed herein a window overlap ratio. The method can further comprisereceiving a third parameter indicative of a desired window overlapratio, and then adjusting one or more parameters of the IGRT system suchthat the actual window overlap ratio becomes closer to the desiredwindow overlap ratio for future members of the time sequence. The one ormore parameters can include, for example, the tomosynthesisreconstruction coverage arc(s), the data aging threshold, an acquisitionrate of the x-ray cone beam projection images, and the time separationbetween future adjacent members of the time sequence.

One or more aspects of the method of FIG. 12, as well as one or moreaspects of the methods of FIG. 18 and FIGS. 19-20 infra, can be carriedout according to one or more of the methods described in one or more ofthe commonly assigned applications incorporated by reference above. Forone preferred embodiment, comparing the latest member of the timesequence of sliding-window tomosynthesis reconstructed image volumeswith the pre-acquired image data set comprises computing a digitallyreconstructed tomosynthesis (DRT) image data set from the pre-acquired3D image volume, processing the DRT image data set to compute a DRTimage volume, and computing a registration between the latest member andthe DRT image volume. Where the latest member of the intrafraction timesequence of tomosynthesis reconstructed image volumes is computed from afirst subset of the population of x-ray cone beam projection images, theDRT image data set is computed from the pre-acquired 3D image volumeusing a virtual projection process, wherein each virtual projection ispreferably based on the imaging geometry associated with a respectivecorresponding one of the first subset of the x-ray cone beam projectionimages.

For one preferred embodiment in which the treatment guidance imagingsystem uses tomosynthesis imaging for both setup and in-treatmentimaging, an initial population of x-ray cone beam projection images isacquired, and a first registration between the initial tomosynthesisvolume and the DRT image volume is carried out. The initial populationof x-ray cone beam projection images is preferably acquired with thebody part in an initial treatment position, or alternatively at someother starting point in time during setup, upon setup, or near abeginning of the treatment delivery, termed herein an initial time.Computation of the registration between the latest member of the timesequence of sliding-window tomosynthesis reconstructed image volumes andthe DRT image volume is based upon (i) the first registration betweenthe initial tomosynthesis image data set and the DRT image volume, and(ii) a second registration between the latest member and the initialtomosynthesis volume. For another preferred embodiment, comparison ofthe latest member of the time sequence of sliding-window tomosynthesisreconstructed image volumes with the pre-acquired image data setcomprises a direct 3D-3D registration between the tomosynthesisreconstructed image volume and the complete 3D pre-acquired imagevolume.

FIG. 19 illustrates image guided radiation treatment usingsliding-window CBCT imaging according to a preferred embodiment. Themethod of FIG. 19 is analogous in many respects to the method of FIG.12, except that the imaging arc over which the population of x-ray conebeam projection images is acquired is at least 180 degrees plus the fanbeam angle of the x-ray cone beam source, i.e., the minimum CBCT arc.Any of the systems of FIGS. 13A-16 can be used in conjunction with themethod of FIG. 19, and the conceptual diagram of FIG. 17 is likewiseapplicable provided that a minimum CBCT arc is traversed in acquiringthe subject subset of x-ray cone beam projection images. Stereo CBCTimaging can be likewise incorporated, with the configuration of FIG. 13Bbeing particularly advantageous.

By way of example and not by way of limitation, the method of FIG. 19 isdiscussed further hereinbelow with respect to the exemplary IGRT system1300 of FIG. 13A. At step 1902, a pre-acquired image data set isreceived. At step 1904, during a patient setup interval, the patient ispositioned into an initial treatment position relative to the IGRTsystem. At step 1906, a first population of x-ray cone beam projectionimages of the body part for a respective first population of gantryangles and acquisition times is acquired, the first population of gantryangles extending at least over a minimum CBCT arc. At step 1908, thefirst population of x-ray cone beam projection images is processed tocompute therefrom a time sequence of sliding-window CBCT reconstructedimage volumes characterized in that each subsequent member of the timesequence is computed using at least one same x-ray cone beam projectionimage that was used in computing at least one previous member of thetime sequence. At step 1910 treatment radiation is delivered to the bodypart based at least in part on a comparison between each of the timesequence of sliding-window CBCT volumes and the pre-acquired image dataset.

Image-guided radiation treatment according to the method of FIG. 19,will usually involve repetition of steps 1906-1910 throughout thetreatment fraction, including the computation of a latest (i.e., mostrecent) member of the time sequence of sliding-window CBCT volumes,comparing that latest member with the pre-acquired image data set, anddelivering treatment radiation to the body part based on the results ofthat comparison. As used herein, the term latest gantry angle refers tothe gantry angle associated with the most recent x-ray cone beamprojection image used to form the latest member of the sequence ofsliding-window CBCT volumes. For one preferred embodiment, computationof the latest member of the sequence comprises identifying from theacquired population of x-ray cone beam projection images a subsetthereof having corresponding gantry angles that are between the minimumCBCT arc and 360 degrees away from the latest gantry angle, andcomputing the latest member based on that first subset.

For another preferred embodiment, computation of the latest member ofthe sequence of CBCT volumes comprises receiving a first parameterindicative of a desired CBCT coverage arc, which must of course begreater than or equal to the minimum CBCT arc, identifying from theacquired population of x-ray cone beam projection images a first subsetthereof having corresponding gantry angles that are within the desiredCBCT coverage arc of the latest gantry angle, and computing the latestmember based on that first subset. The CBCT coverage arc will usually bebetween the minimum CBCT arc and 360 degrees. As used herein, latestacquisition time refers to the time of acquisition of the most recentx-ray cone beam projection image used to form the latest member of thesequence of sliding-window CBCT volumes. For one preferred embodiment,computation of the latest member of the sequence comprises receiving asecond parameter indicative of a desired data aging threshold,identifying from the first subset of x-ray cone beam projection images asecond subset thereof having corresponding acquisition times that arewithin the desired data aging threshold of the latest acquisition time,and computing the latest member using only that second subset of x-raycone beam projection images.

As with the tomosynthesis-based method supra, the method of FIG. 19 canfurther comprise evaluating the percentage of x-ray ray cone beamprojection images that are being re-used between the latest member ofthe time sequence of sliding-window CBCT volumes and the immediatelypreceding member of the sequence (window overlap ratio), and thenadjusting one or more parameters of the IGRT system such that the actualwindow overlap ratio becomes closer to the desired window overlap ratiofor future members of the time sequence. The one or more parameters caninclude, for example, the CBCT coverage arc(s), the data agingthreshold, an acquisition rate of the x-ray cone beam projection images,and the time separation between future adjacent members of the timesequence.

For one preferred embodiment, comparing the latest member of the timesequence of sliding-window CBCT image volumes, which is referencedherein as CBCT(t), with the pre-acquired image data set comprisescomputing a direct 3D-3D registration between CBCT(t) and thepre-acquired 3D image volume. However, as with the tomosynthesis-basedmethod supra, the method of FIG. 19 can alternatively leverage theadvantages of a preferred registration scheme in which a “bridging”registration between image volumes acquired with different acquisitionsystems having different frames of reference only needs to be computedonce per treatment fraction, and in which only “non-bridging”registrations need to be performed during the treatment fraction afterthe beginning of radiation delivery. Thus, for one preferred embodimentin which the treatment guidance imaging system uses CBCT imaging forboth setup and in-treatment imaging, an initial population of x-ray conebeam projection images is acquired, an initial CBCT volume CBCT(0) isformed, and a first registration between CBCT(0) and the pre-acquiredimage volume is carried out. Subsequently, comparison of CBCT(t) againstthe pre-acquired image data set can be carried out by computing a secondregistration between CBCT(t) and CBCT(0), and then registering CBCT(t)to the pre-acquired image data set based on (i) the first registrationbetween CBCT(0) and the pre-acquired 3D image volume, and (ii) thesecond registration between CBCT(t) and CBCT(0).

FIG. 20 illustrates image guided radiation treatment using x-ray sourcearrays according to a preferred embodiment. Any of the systems of FIGS.13A-16 can be used in conjunction with the method of FIG. 20, providedthere is at least one x-ray source array (XSA) included. Although notrequired for all cases, it is preferable that the x-ray source array XSAbe dimensioned and configured within the imaging geometry of thetreatment guidance imaging system such a tomosynthesis imaging arc of atleast about 6 degrees can be provided by virtue of the spatialdistribution of the x-ray point sources thereon, without requiring anyrotation of the rotatable gantry structure. At step 2002, a pre-acquiredimage data set is received. At step 2004, during a patient setupinterval, the patient is positioned into an initial treatment positionrelative to the IGRT system. At step 2006, at a first gantry angle, thex-ray source array XSA is operated to acquire a population of x-ray conebeam projection images of the body part. At step 2008, the firstpopulation of x-ray cone beam projection images is processed to computea tomosynthesis reconstructed image volume. At step 2010, treatmentradiation is delivered to the body part based at least in part on acomparison between the tomosynthesis reconstructed image volume and thepre-acquired image data set. Advantageously, meaningful 3D-based imageguidance can be provided even where the rotatable gantry structure isstationary. This may be particularly useful in scenarios in which thetreatment guidance system is attached to the same rotatable gantrystructure as the radiation treatment head, and in which the radiationtreatment plan requires the rotatable gantry structure to remainstationary for a period of time.

One or more aspects of the method of FIG. 20 can be carried outaccording to one or more of the methods described in the commonlyassigned and concurrently filed Atty. Docket No. AR-004A-PROV, supra.For one preferred embodiment, comparing the intrafraction tomosynthesisreconstructed image, designated hereinbelow as tomo(t), with thepre-acquired image data set comprises computing a digitallyreconstructed DRT image data set from the pre-acquired 3D image volume,processing the DRT image data set to compute a DRT image volume, andcomputing a registration between tomo(t) and the DRT image volume.Preferably, the DRT image data set is computed from the pre-acquired 3Dimage volume using virtual projections based on the same imaginggeometry for which tomo(t) was acquired.

For one preferred embodiment in which the treatment guidance imagingsystem uses tomosynthesis imaging for both setup and in-treatmentimaging, an initial tomosynthesis image volume tomo(0) is acquired, anda first registration between tomo(0) and a DRT image volume based on thepre-acquired image data set is carried out. The x-ray cone beamprojection images from which tomo(0) is reconstructed are preferablyacquired with the body part in an initial treatment position, oralternatively at some other starting point in time during setup, uponsetup, or near a beginning of the treatment delivery, termed herein aninitial time. Computation of the registration between tomo(t) and theDRT image volume is then based upon (i) the first registration betweentomo(0) and the DRT image volume, and (ii) a second registration betweentomo(t) and tomo(0).

For another preferred embodiment, comparison of tomo(t) to thepre-acquired image data set comprises a direct 3D-3D registrationbetween tomo(t) and the pre-acquired image volume. For another preferredembodiment, the method of FIG. 18 can be used in conjunction with themethod of FIG. 20, wherein an initial population of x-ray cone beamprojection images is acquired at an initial time and used to constructan initial CBCT volume CBCT(0). A first registration is then performedbetween CBCT(0) and the pre-acquired image data set. During radiationdelivery, for the most recent tomosynthesis volume tomo(t), there isidentified a subset of the initial population of x-ray cone beamprojection images that were used to construct CBCT(0) that correspond intomosynthesis imaging arc to the tomosynthesis imaging arc for tomo(t),and an arc-MATCHED tomosynthesis volume tomo_(MATCHED(t))(0) is computedtherefrom. A second registration between tomo(t) andtomo_(MATCHED(t))(0) is computed, and then the desired registrationbetween tomo(t) and the pre-acquired image volume is computed based on(i) the first registration between CBCT(0) and the pre-acquired imagevolume, (ii) the inherent registration between tomo_(MATCHED(t))(0) andCBCT(0), and (iii) the second registration between tomo(t) andtomo_(MATCHED(t))(0).

According to yet another preferred embodiment that can be used inconjunction with one or more of the above-described preferredembodiments, an IGRT system having dynamic switching capability betweensliding-window tomosynthesis-based treatment guidance and sliding-windowCBCT-based treatment guidance is provided. Subsequent to a patient setupinterval, an x-ray cone beam imaging source and it associated detectorare operated to acquire a population of x-ray cone beam projectionimages of the body part for a respective population of gantry angles andacquisition times. First information is received that is indicative of aselection between a tomosynthesis-based treatment guidance mode ofoperation and a CBCT-based treatment guidance mode. The first populationof x-ray cone beam projection images is processed to compute therefrom atime sequence of sliding-window tomographic image volumes characterizedin that each subsequent member of the time sequence is computed using atleast one same x-ray cone beam projection image as used in computing atleast one previous member of that time sequence, wherein thesliding-window tomographic image volume comprises one of (i) atomosynthesis reconstructed image volume if the first informationindicates the tomosynthesis-based treatment guidance mode, and (ii) aCBCT image volume if the first information indicates the CBCT-basedtreatment guidance mode. The radiation treatment head is operated todeliver treatment radiation to the body part based at least in part on acomparison between each of the time sequence of sliding-windowtomographic image volumes and the pre-acquired image data set.

Optionally, the selection between tomosynthesis-based mode andCBCT-based mode is automatically and dynamically determined duringradiation treatment delivery. A selection algorithm can be provided thatmakes the selection based upon one or more of: a data aging threshold;an acquisition rate of the x-ray cone beam projection images; a timeseparation between adjacent members of the time sequence; a rotationalmovement pattern of the rotatable gantry structure; an available numberof x-ray cone beam projection images acquired within the data agingthreshold of a most recent x-ray cone beam projection image acquisition;and a gantry angle distribution associated with the available number ofx-ray cone beam projection images acquired within the data agingthreshold of the most recent x-ray cone beam projection imageacquisition. User inputs indicative of certain thresholds to be used inthe decision process and/or operator overrides can optionally beprovided.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that theparticular embodiments shown and described by way of illustration are inno way intended to be considered limiting. By way of example, althoughone or more preferred embodiments are described above in which thein-therapy imaging sources are distinct from the therapeutic radiationsource, in other preferred embodiments the imaging system can beprovided as a portal imaging system, in which an imaging detector isprovided opposite the therapeutic radiation source relative to theisocenter.

By way of further example, with nonlimiting exemplary reference to FIG.3B, supra, while the beam members 306 of the rotatable gantry structure304 are described as extending between ring members 308 and 309 that areon opposite sides of the isocentric transverse plane 217, it is notoutside the scope of the present teachings to provide a system in whichthe opposing ring members are on the same side of the isocentrictransverse plane. In such cases, the opposing ring members would beseparated by an amount sufficient to ensure mechanical stability (forexample, 1 m-2 m depending on the choice of materials or other designcriteria), while the isocenter could be positioned slightly outside theend of the central bore, which could potentially be useful for sometherapy scenarios now known or hereinafter developed.

By way of still further example, the above-described teaching in whichtwo kV imaging systems are mounted perpendicular to each other andacquire all of the X-ray images required for CBCT image reconstructionwith only a 90 degree rotation, rather than a 180 degree rotation, of arotatable structure on which they are mounted can be used on systemswith a variety of different overall mechanical architectures, andtherefore is within the scope of the present teachings as applied to avariety of different suitable overall architectures other than theparticularly suitable mechanical architectures described hereinabove. Byway of even further example, the teachings above relating to slidingCBCT reconstruction can be used on systems with a variety of differentoverall suitable mechanical architectures, and therefore is within thescope of the present teachings as applied to a variety of differentoverall suitable architectures other than the particularly suitablemechanical architectures described hereinabove. Therefore, reference tothe details of the embodiments are not intended to limit their scope,which is limited only by the scope of the claims set forth below.

What is claimed is:
 1. A radiation treatment apparatus, comprising: agantry frame; a rotatable gantry structure rotatably coupled to thegantry frame, the rotatable gantry structure being rotatable around arotation axis passing through an isocenter, the rotatable gantrystructure comprising a first beam member extending between first andsecond ends of the rotatable gantry structure; and a radiation treatmenthead movably mounted to the first beam member in a manner that allows(i) translation of the radiation treatment head along the first beammember between the first and second ends, and (ii) gimballing of theradiation treatment head relative to the first beam member, thegimballing comprising pivotable movement in at least two independentpivot directions defined with respect to the first beam member, whereinthe rotatable gantry structure is rotably coupled and radiationtreatment head is movably mounted to provide non-coplanar radiationtreatment of a tissue volume positioned near or around the isocenter. 2.The radiation treatment apparatus of claim 1, the rotatable gantrystructure further comprising first and second ring members correspondingto the first and second ends, respectively, and wherein the first andsecond ring members are rotatable around the rotation axis, the firstbeam member being fixably coupled to the first and second ring members.3. The radiation treatment apparatus of claim 1, a transverse isocentricplane being defined that passes through the isocenter in a directionorthogonal to the rotation axis, wherein the at least two independentpivot directions include a first pivot direction around a first pivotaxis generally parallel to the transverse isocentric plane and a secondpivot direction around a second pivot axis nonparallel to the firstpivot axis.
 4. The radiation treatment apparatus of claim 1, furthercomprising an imaging system comprising an imaging source and an imagingdetector, wherein the imaging source and imaging detector are fixablymounted on the gantry frame at opposing positions relative to theisocenter.
 5. The radiation treatment apparatus of claim 4, wherein theimaging system comprises a first imaging source, a second imagingsource, and first and second imaging detectors respectively opposite thefirst and second imaging sources, wherein the first imaging source andthe second imaging source are mounted to obtain stereo images of theisocenter at a non-zero angle relative to each other.
 6. The radiationtreatment apparatus of claim 1, the rotatable gantry structurecomprising second and third beam members distal from the rotation axisand extending between the first and second ends, wherein the second andthird beam members are disposed generally opposite each other relativeto the rotation axis, and wherein the radiation treatment apparatusfurther comprises an imaging system including an imaging source mountedon the second beam member and an imaging detector mounted on the thirdbeam member.
 7. The radiation treatment apparatus of claim 1, therotatable gantry structure being a first rotatable gantry structure, andwherein the radiation treatment apparatus further comprising: a secondrotatable gantry structure rotatably coupled to the gantry frame, thesecond rotatable gantry structure being rotatable around the rotationaxis concentrically with, and independently of, the first rotatablegantry structure; the second rotatable gantry structure comprisingsecond and third beam members each distal from the rotation axis andextending between opposing ends thereof, the second and third beammembers being disposed generally opposite each other relative to therotation axis; and an imaging system comprising an imaging sourcepositioned on the second beam member and an imaging detector positionedon the third beam member.
 8. The radiation treatment apparatus of claim7, the imaging source being a first imaging source and the imagingdetector being a first imaging detector, wherein the imaging systemcomprises: a second imaging source; and a second imaging detectoropposite the second imaging source, wherein the first imaging source andthe second imaging source are mounted to obtain stereo images of theisocenter at a non-zero angle relative to each other.
 9. The radiationtreatment apparatus of claim 7, a transverse isocentric plane beingdefined that passes through the isocenter in a direction orthogonal tothe rotation axis, wherein the imaging source is translatable along thesecond beam member between the first and second ends, and wherein theimaging detector is translatable along the third beam member between thefirst and second ends, wherein the imaging system is configured to imagethe tissue volume at a plurality of different imaging angles relative tothe transverse isocentric plane.
 10. The radiation treatment apparatusof claim 1, wherein the first beam member is movable away from therotation axis to increase a distance between the radiation treatmenthead and the rotation axis, and wherein the first beam member is movabletoward the rotation axis to decrease the distance between the radiationtreatment head and the rotation axis.
 11. The radiation treatmentapparatus of claim 1, further comprising a patient couch operativecoupled in the radiation treatment apparatus in manner to providemovement of the couch relative to the radiation treatment head.
 12. Theradiation treatment apparatus of claim 1, further comprising acontroller operatively coupled with the patient couch and the radiationtreatment head to control movement of the patient couch and gimbaling ofthe radiation treatment head.